BEGIN:VCALENDAR PRODID:University of Cologne\, ITP\, Events Server X-WR-TIMEZONE:Europe/Berlin BEGIN:VEVENT SUMMARY:QM2 | Charles Marcus DTSTART;TZID=Europe/Berlin:20130508T143000 DTEND;TZID=Europe/Berlin:20130508T160000 DTSTAMP:20260527T090435Z UID:0000000984@events.thp.uni-koeln.de DESCRIPTION:Charles Marcus\, Center for Quantum Devices\, University of Co penhagen\n\nHas Majorana returned\, and why we should care\n\n\n\nContact Person: Achim Rosch LOCATION:Lecture Hall 3 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dr. Ar­ka­dy Kras­hen­ni­ni­kov DTSTART;TZID=Europe/Berlin:20130515T143000 DTEND;TZID=Europe/Berlin:20130515T153000 DTSTAMP:20260527T090435Z UID:0000000272@events.thp.uni-koeln.de DESCRIPTION:Dr. Ar­ka­dy Kras­hen­ni­ni­kov\, Uni­ver­si­ty of He l­sin­ki\n\nNa­ti­ve and ir­ra­dia­ti­on-in­du­ced de­fects in two-di­men­sio­nal ma­te­ri­als: gra­phe­ne\, bo­ron-ni­tri­de\ , tran­si­ti­on metal dich­a­col­gen­ides\, and si­li­ca\n\n\n\nC ontact Person: Tho­mas Mi­che­ly LOCATION:Se­mi­nar room of the In­sti­tu­te of Phy­sics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Prof. Nicolai Reshetikhin DTSTART;TZID=Europe/Berlin:20130529T143000 DTEND;TZID=Europe/Berlin:20130529T153000 DTSTAMP:20260527T090435Z UID:0000000257@events.thp.uni-koeln.de DESCRIPTION:Prof. Nicolai Reshetikhin\, Berkeley\n\nOn semiclassical quant ization of gauge theories on space time manifolds with boundary\n\nIt is w ell known how to construct a formal semiclassical (or perturbative) quanti zation of a classical field theory on $\\R^n$. The answer is given by form al power series in Feynman diagrams. In this talk we will focus on how to do it for space time manifolds with boundary. The main example is Chern-Si mons classical field theory. The talk is based on joint work with A. Catta neo and P. Mnev. \n\nContact Person: Peter Littelmann LOCATION:Seminar room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Prof. Herbert Spohn DTSTART;TZID=Europe/Berlin:20130605T143000 DTEND;TZID=Europe/Berlin:20130605T160000 DTSTAMP:20260527T090435Z UID:0000000256@events.thp.uni-koeln.de DESCRIPTION:Prof. Herbert Spohn\, TU München\n\nNonlinear fluctuating hyd rodynamics and anharmonic chains\n\nRather commonly\, Hamiltonian systems at nonzero temperature\nin one spatial dimension have short range static c orrelations\, but\nlong-lived excitations. The slowest modes are the local ly conserved fields.\nTo capture their universal behavior we develop a non linear version of\nfluctuating hydrodynamics. The best studied systems are classical\nanharmonic chains. We compare with MD simulations.\n\n\nContac t Person: Markus Kunze LOCATION:Seminar room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dr. Oleg Petracic DTSTART;TZID=Europe/Berlin:20130619T143000 DTEND;TZID=Europe/Berlin:20130619T153000 DTSTAMP:20260527T090435Z UID:0000000273@events.thp.uni-koeln.de DESCRIPTION:Dr. Oleg Petracic\, Forschungszentrum Jülich\n\nStructural an d magnetic correlations of self-assembled nanoparticle superlattices\n\nNa noparticle superlattices can be considered as novel type of materials with controllable electronic\, optical and magnetic properties. Their building blocks are nanoparticles (or 'nanocrystals') from a metallic\, metal-oxid e\, or semiconducting material or hybrid between different materials. I wi ll report about the structural and magnetic properties of 2- or 3-dimensio nal 'superlattices' of magnetic nanoparticles. Depending on the substrate and the self-assembly technique we can fabricate either 'superlattice film s' showing various growth modes as known from classical thin films or 3d m esocrystals. The lateral ordering is quantified using electron microscopy and grazing incidence small angle X-ray scattering (GISAXS). The magnetic behavior and correlations are investigated by magnetometry\, polarized neu tron reflectometry (PNR) and grazing incidence small-angle neutron scatter ing (GISANS).\n\nContact Person: Markus Grüninger LOCATION:Seminar room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Manuel Brando DTSTART;TZID=Europe/Berlin:20130717T143000 DTEND;TZID=Europe/Berlin:20130717T153000 DTSTAMP:20260527T090435Z UID:0000000274@events.thp.uni-koeln.de DESCRIPTION:Manuel Brando\, MPI CPfS Dresden\n\nFerromagnetic quantum crit icality in heavy fermion systems\n\nHeavy fermion (HF) systems are metals where the weak hybridisation between nearly localized f-electrons and the mobile conduction electrons\, i.e. the Kondo e ect\, leads to a Fermi liqu id (FL) ground state with narrow bands and quasiparticles with strongly en hanced e ective electronic masses. When the magnetic RKKY interaction beco mes comparable to the Kondo interaction\, magnetic order can appear\, most ly at very low T. The magnetic order can be suppressed by an external para meter\, e.g. pressure or magnetic eld\, inducing a quantum phase transiti on (QPT) at T = 0. If this QPT is continuous\, the associated quantum crit ical point (QCP) is surrounded by a non- FL regime of quantum critical fuc tuations where unconventional superconductivity or novel phases of matter may arise [1].\n\nThe unambiguous observation of antiferromagnetic (AFM) Q CPs in HF systems [2] has led to an increasing number of theoretical and e xperimental works in order to understand QPTs as deeply as their classical counterpart. Although it has been demonstrated that in antiferromagnets Q CPs exist\, in ferromagnets there is still no clear evidence. Intensive in vestigations have shown that metallic ferromagnets are inherently unstable [3\, 4] and do not exhibit a FM QCP.\n\nHowever\, in the recently discove red HF system YbNi4P2\, a quasi-1D ferromagnet with a remarkably-low TC = 0:15K [5\, 6]\, the T-divecgence in the Grüneisen ratio [7] points to the presence of a FM QCP. I will present a general overview of the state of t he art of FM quantum criticality in HF systems\, discussing in particular the cases of YbNi4P2 [5\, 6]\, CeFePO [8]\, CePd1-xRhx [9] as well as the AFM system YbRh2Si2 [10] where FM order is induced by chemical pressure [1 1].\n\n \n\nContact Person: Markus Garst LOCATION:Seminar room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Test Speaker DTSTART;TZID=Europe/Berlin:20130907T100000 DTEND;TZID=Europe/Berlin:20130907T120000 DTSTAMP:20260527T090435Z UID:0000000269@events.thp.uni-koeln.de DESCRIPTION:Test Speaker\, Test Affiliation\n\nTest talk\n\ntest test test test\n\nContact Person: Contact Test LOCATION:nowhere END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Erez Berg DTSTART;TZID=Europe/Berlin:20131106T143000 DTEND;TZID=Europe/Berlin:20131106T160000 DTSTAMP:20260527T090435Z UID:0000000278@events.thp.uni-koeln.de DESCRIPTION:Erez Berg\, Weizmann Institute\n\nThere's Life at Absolute Zer o: Exotic Phases of Quantum Matter\n\nTraditionally\, condensed matter phy sicists have classified phases of\nmatter according to their symmetries. O ver the last few decades\, it\nbecame clear that near zero temperature\, t here are plenty of phases\nwhich lie beyond this classification scheme. Th ese intrinsically\nquantum mechanical states of matter lack any ordinary o rder parameter\;\nthey can be thought of as a strongly fluctuating quantum liquids.\nNevertheless\, they posses a hidden underlying order\, known as \n"topological order". The quantum Hall effect is a celebrated example\nof such a phase\; several others have been discovered recently\, and\nmany m ore have been predicted theoretically. The elementary\nexcitations of topo logically ordered states can be thought of as\nemergent particles\; intrig uingly\, these particles can obey unusual\nexchange statistics rules which resemble neither those of bosons nor\nof fermions. This property makes to pological phases potentially useful\nas building blocks for future decoher ence-free quantum processing\ndevices. In this talk\, I will describe some modern insights into the\nnature of these phases\, and their characteriza tion in term of their\nquantum entanglement. I will also discuss a new rou te to realize novel\nphases that arise on the boundaries of other\, previo usly known\ntopologically ordered states.\n\n\nContact Person: Simon Trebs t LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Anton Akhmerov DTSTART;TZID=Europe/Berlin:20131113T143000 DTEND;TZID=Europe/Berlin:20131113T160000 DTSTAMP:20260527T090435Z UID:0000000282@events.thp.uni-koeln.de DESCRIPTION:Anton Akhmerov\, TU Delft\n\nCoulomb manipulation of Majorana fermions with superconducting circuits\n\nCreation of isolated Majorana fe rmions\, the simplest type of\nnon-Abelian anyons\, in one out of many sup erconductor-semiconductor\nhybrid systems seems reachable within a few yea rs time.\nI will introduce a scheme for manipulation of Majorana fermions using\nexistent superconducting circuits\, namely transmon qubits.\nWithin this framework I will consider in particular the minimal setup\nrequired to measure the unusual properties of Majorana fermions\, and a\npossible i mplementation of a scalable quantum computer that relies on\nthe topologic al properties of Majorana fermions.\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Montu Saxena DTSTART;TZID=Europe/Berlin:20131118T100000 DTEND;TZID=Europe/Berlin:20131118T103000 DTSTAMP:20260527T090435Z UID:0000000283@events.thp.uni-koeln.de DESCRIPTION:Montu Saxena\, University of Cambridge\n\nQuantum Criticality and Superconductivity in Spin and Charge Systems\n\nThis talk will focus o n experimental search and discovery of novel forms of quantum order in met allic and insulating magnets\, intercalated compounds\, ferroelectric syst ems and multi-ferroic materials. Particularly discussed will be the pressu re-induced superconductivity and critical phenomena in the vicinity of qua ntum\nphase transitions.\n\nMaterials tuned to the neighbourhood of a zero temperature phase transition often show the emergence of novel quantum ph enomena. Much of the effort to study these new emergent effects\, like the breakdown\nof the conventional Fermi-liquid theory in metals has been foc used in narrow band electronic systems. But Spin or Charge ordered phases in insulating systems can also be tuned to absolute zero using hydrostatic pressure. Close to such a zero temperature phase transition\, physical qu antities like resistivity\, magnetisation and dielectrics constant change into radically unconventional forms due to the fluctuations experienced in this region giving rise to new kinds ordered states including superconduc tivity in the metallic systems\n\n\nContact Person: Paul H.M. van Loosdrec ht LOCATION:Seminar Room A\, Institute of Chemistry END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Jure Demsar DTSTART;TZID=Europe/Berlin:20131120T143000 DTEND;TZID=Europe/Berlin:20131120T160000 DTSTAMP:20260527T090435Z UID:0000000293@events.thp.uni-koeln.de DESCRIPTION:Jure Demsar\, Ilmenau University of Technology\n\nThe interpla y between the electronic and lattice degrees of freedom in Density Waves probed with femtosecond real-time probes\n\nIn many of the advanced solids exhibiting macroscopic quantum phenomena (e.g. superconductivity) their f unctional properties arise from a delicate balance between interactions am ong different degrees of freedom (electrons\, phonons\, spins). An example of such is the appearance of Charge Density Wave (CDW) ground state in se veral quasi one- or two-dimensional metals. According to the standard Peie rls’ scenario the appearance of the CDW phase is driven by the divergent static electronic susceptibility at a wave vector q=2k­F. This classical description has been challenged [1]\, arguing that the appearance of CDWs \, in particular in the transition-metal dichalcogenides\, is due to stron g (q-dependent) electron-phonon coupling [1].\n\nI will review some recent studies where some of the open questions were addressed utilizing femtose cond time-resolved optical [2] and structural probes [3-5]. Using femtosec ond electron diffraction we were able to directly follow the photo-trigger ed dynamics of the periodic lattice distortion (order parameter) in dichal cogenides [3\,4]\, point out the importance of three-dimensionality for th e existence of CDWs in these quasi-2D systems [4]\, and to track the diffe rent stages of the photo-induced phase transition between different CDW ph ases [5].\n\n[1] e.g. M. Johannes and I. Mazin\, Phys. Rev. B 77 (2008)\; L. Gor'kov\, Phys. Rev. B 85\, 165142 (2012)\; H-M. Eiter\, PNAS 110\, 64 (2013).\n[2] H. Schäfer\, et al.\, Phys. Rev. Lett. 105\, 066402 (2010)\; H. Schäfer\, et al.\, EPJ-ST 222\, 1005 (2013).\n[3] M. Eichberger\, et al.\, Nature 468\, 799 (2010).\n[4] N. Erasmus\, et al.\, Phys. Rev. Lett. 109\, 167402 (2012)\; E. Eichberger\, et al.\, APL 102\, 121106 (2013).\n [5] K. Haupt\, et al.\, in preparation.\n\nContact Person: Paul H.M. van L oosdrecht LOCATION:Seminar Room\, Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Alexander Brinkmann DTSTART;TZID=Europe/Berlin:20131127T143000 DTEND;TZID=Europe/Berlin:20131127T160000 DTSTAMP:20260527T090435Z UID:0000000284@events.thp.uni-koeln.de DESCRIPTION:Alexander Brinkmann\, University of Twente\n\nTransport and su perconductivity at topological surfaces and interfaces\n\nDue to the locki ng of the electron spin to the momentum at the conducting surface of a 3D topological insulator\, new physical phenomena arise in transport and supe rconductivity. The topological nature of surface states can be evidenced b y measuring the Berry phase of quantum oscillations in magnetotransport. I will quickly review the current status of the Bi-based class of 3D topolo gical insulators in terms of how good a topological insulator one can make nowadays. Also the conducting interface between insulating LaAlO3 and SrT iO3 bears great resemblance to these topological surfaces.\nWhen supercond uctivity is induced into a topological state by using the proximity effect or a Josephson junction configuration\, the superconducting order paramet er can have a large p-wave component\, leading to Andreev bound states at zero energy\, the so-called Majorana states. I will review the status of o ur experiments on topological Josephson junctions based on the Bi-based 3D topological insulators\, as well as conducting interfaces between LaAlO3 and SrTiO3.\n\nContact Person: Paul H.M. van Loosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Steve Zelditch DTSTART;TZID=Europe/Berlin:20131211T143000 DTEND;TZID=Europe/Berlin:20131211T160000 DTSTAMP:20260527T090435Z UID:0000000285@events.thp.uni-koeln.de DESCRIPTION:Steve Zelditch\, Northwestern University\n\nShapes and Sizes o f Eigenfunctions \n\nEigenfunctions of the Schrodinger operator (or a La placian on a domain or manifold)\nrepresent modes of vibrations of drums a nd membranes. In quantum mechanics\nthey represent stationary states of a toms. Understanding shapes and sizes of\neigenfunctions allows one to visu alize these objects. An intriguing problem\nis to relate the shapes and si zes of eigenfunctions to the underlying classical mechanics\,\nsuch as the geodesic flow of (M\, g) or the dynamics of billiard trajectories\non a b illiard table. \n\nIn this talk we will explain the role of eigenfunctions in quantum mechanics\nand discuss both classic and new results describing nodal (zero) sets\nof eigenfunctions. The new results relate nodal sets to classical dynamics. \nNo prior knowledge of quantum mechanics is assume d. \n\n\nContact Person: George Marinescu LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Jan Seidel DTSTART;TZID=Europe/Berlin:20140114T120000 DTEND;TZID=Europe/Berlin:20140114T133000 DTSTAMP:20260527T090435Z UID:0000000324@events.thp.uni-koeln.de DESCRIPTION:Jan Seidel\, Universität New South Wales\n\nDomain wall funct ionality in complex oxides\n\n\n\nContact Person: Paul LOCATION:Seminarraum Kernphysik END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Michael Kiessling DTSTART;TZID=Europe/Berlin:20140115T143000 DTEND;TZID=Europe/Berlin:20140115T160000 DTSTAMP:20260527T090435Z UID:0000000287@events.thp.uni-koeln.de DESCRIPTION:Michael Kiessling\, Rutgers University\n\nAtoms with Bosonic ' Electrons'\n\nAtoms with bosonic `electrons' have always been more of a\nt heoretical fancy than a model of real physical matter\, at best suited to\ nillustrate how important the Pauli principle is in our world\, but mainly \nof only academic interest to mathematical physicists. All this is about to\nchange in the not-too-distant future if the recently discovered anti-a lpha\nparticles (anti-He nuclei which are twice positively charged bosons in\ntheir nuclear ground state) can be produced in sufficiently large numb ers\,\ncaptured\, and substituted for the conventional electrons in the at omic\nhull around conventional nuclei (a similar feat has already been\nac complished with anti-protons\, but these are fermions\, not bosons). In my \ntalk I will try to survey what is mathematically rigorously known about\ natoms with bosonic `electrons' and\, more importantly\, present a list of \ninteresting open problems which still await their solution.\n\n\nContact Person: Markus Kunze LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Sebastian Gönnewein DTSTART;TZID=Europe/Berlin:20140122T150000 DTEND;TZID=Europe/Berlin:20140122T163000 DTSTAMP:20260527T090435Z UID:0000000329@events.thp.uni-koeln.de DESCRIPTION:Sebastian Gönnewein\, TU München\n\nSpin Currents in Ferroma gnet / Normal Metal Hybrid Structures\n\n\n\nContact Person: Paul H.M. van Loosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dr. Jeroen Custers DTSTART;TZID=Europe/Berlin:20140129T143000 DTEND;TZID=Europe/Berlin:20140129T160000 DTSTAMP:20260527T090435Z UID:0000000314@events.thp.uni-koeln.de DESCRIPTION:Dr. Jeroen Custers\, Charles University\, Prague\n\nSupercondu ctivity emerging in the magnetic state in heavy fermion materials Ce3PdIn1 1 and Ce3PtIn11 at ambient pressure\n\nThe present focus on quantum critic al phenomena in correlated matter is driven by the puzzling enigma concern ing the origin of unconventional superconductivity (SC). In a weak couplin g picture\, the magnetic ordering is a spin density wave (SDW) induced by Fermi surface (FS) nesting of itinerant electrons. Consequently\, supercon ductivity results from pair scattering between the electron - and holelike FS pockets. A drastically different viewpoint proposes that magnetism and superconductivity develop out of localized moments which are generated by strong electron - electron correlations (strong coupling limit). The simi larities in the superconducting phase diagrams of correlated materials tem pt us to believe that there may be a certain fundamental aspects shared be tween the iron pnictides\, chalcogenides\, cuprate superconductors and the HF materials. Against this backdrop\, heavy Fermion (HF) materials acquir e a new significance.\n\nThis class of materials is inherent close to a ma gnetic quantum phase transition frequently in conjunction with emergence o f unconventional superconductivity [1]. Recently it was shown that strong and weak coupling scenarios are complementary if taking into account the " dimensionality" of the critical fluctuations which in most cases mirrors t he structural dimensionality of the compound [2-4]. In this presentation I will discuss the global phase diagram of heavy fermions with an experimen tal focus on the CenTmIn3n+2m (T = transition metal\, n = 1\, 2\,..\; m = 0\, 1\,..) family. This family is predestinated in order to understand how magnetism and superconductivity is influenced when going from 3D to 2D HF structures. CenTmIn3n+2m compounds display both attributes with cubic CeI n3 at the 3D and CeCoIn5 as an example of the opposite (2D) end of the ser ies. I will present first results on single crystals of two new members Ce 3PdIn11 and Ce3PtIn11 located in between [5]. At ambient pressure supercon ductivity emerges in the complex antiferromagnetic state below Tc = 0.42 K (Tc = 0.32 K) in Ce3PdIn11 (Ce3PtIn11). Both phenomena coexist in a wide range of the pressure - temperature phase diagrams. The critical pressure where TN -> 0 and Tc is maximum equals pc ~= 1.6 GPa.\n\n[1] H. von Löhne ysen et al.\, Rev. Mod. Phys. 79\, 1015 - 1075 (2007).\n[2] Q. Si\, Physic a B 378-380\, 23 (2008)\n[3] J. Custers et al. Phys. Rev. Lett. 104\, 1864 02 (2010)\n[4] J. Custers et al. Nature Mat. 11\, 189 (2012)\n[5] J. Prokl eska et al. submitted to Science (2013)\n\n\nContact Person: Mohsen Abd-El meguid LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Peter Hirschfeld DTSTART;TZID=Europe/Berlin:20140205T143000 DTEND;TZID=Europe/Berlin:20140205T160000 DTSTAMP:20260527T090435Z UID:0000000292@events.thp.uni-koeln.de DESCRIPTION:Peter Hirschfeld\, University of Florida\n\nNovel Disorder Eff ects in Fe-Based Superconductors\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Yoichi Ando DTSTART;TZID=Europe/Berlin:20140212T100000 DTEND;TZID=Europe/Berlin:20140212T113000 DTSTAMP:20260527T090435Z UID:0000000330@events.thp.uni-koeln.de DESCRIPTION:Yoichi Ando\, Universität Osaka\n\nTopological Insulators and Superconductors: Materials Frontier\n\n\n\nContact Person: Paul H.M. van Loosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Kamran Behnia DTSTART;TZID=Europe/Berlin:20140213T130000 DTEND;TZID=Europe/Berlin:20140213T143000 DTSTAMP:20260527T090435Z UID:0000000336@events.thp.uni-koeln.de DESCRIPTION:Kamran Behnia\, ESPCI Paris\n\nSuperconductivity in dilute met als\n\n\n\nContact Person: not specified LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Klas Lindfors DTSTART;TZID=Europe/Berlin:20140219T143000 DTEND;TZID=Europe/Berlin:20140219T160000 DTSTAMP:20260527T090435Z UID:0000000318@events.thp.uni-koeln.de DESCRIPTION:Klas Lindfors\, Universität zu Köln\n\nOptical antennas for controlling light \n\nResonant plasmonic metal nanoparticles allow manipul ating optical fields on the nanoscale. In analogy to the radio frequency d omain such particles are called optical antennas. They have led to a multi tude of breakthroughs\, e.g.\, in enhancement of light emission and radiat ion engineering of single photons\, as well as ultrasensitive sensing. I w ill present the results of our work on enhancing the optical properties of single solid-state quantum emitters using optical antennas and on applyin g plasmonic nanoantennas in point-to-point links. Coupling a quantum emitt er to the antenna allows enhancing both its absorption efficiency as well as emission rate. Meanwhile\, point-to-point links based on optical antenn as are a promising concept to transmit optical signals between nano-object s. I will show the first realization of such a link. \n\nContact Person: n ot specified LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dionisios Margetis DTSTART;TZID=Europe/Berlin:20140224T143000 DTEND;TZID=Europe/Berlin:20140224T160000 DTSTAMP:20260527T090435Z UID:0000000335@events.thp.uni-koeln.de DESCRIPTION:Dionisios Margetis\, University of Maryland at College Park \n \nBose-Einstein condensation: Pair excitation and many-body bound state of periodic microstructure \n\nThis talk focuses on aspects of Bose-Einstein condensation in a trapped\, dilute atomic gas beyond the Gross-Pitaevskii mean field regime. By use of the formalism of pair excitation introduced by Wu\, based on earlier works by Lee\, Huang and Yang\, the description o f many-body bound states is\naddressed via formal asymptotics. There are t wo related questions to be discussed. \n(i) What is a plausible modeling o f pair correlations by use of Partial Differential Equations\, beyond the Gross-Pitaevskii limit? \n(ii) What is the effective depletion of the macr oscopic quantum state (condensate) for a spatially varying scattering leng th having a periodic microstructure? \n\nContact Person: Joachim Krug LOCATION:Seminar Room of the Institute for Theoretical Physics END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Andew Mackenzie DTSTART;TZID=Europe/Berlin:20140226T143000 DTEND;TZID=Europe/Berlin:20140226T160000 DTSTAMP:20260527T090435Z UID:0000000288@events.thp.uni-koeln.de DESCRIPTION:Andew Mackenzie\, University of St. Andrews\n\nt.b.a.\n\n\n\nC ontact Person: Markus Braden LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Roderick MacKenzie DTSTART;TZID=Europe/Berlin:20140313T143000 DTEND;TZID=Europe/Berlin:20140313T160000 DTSTAMP:20260527T090435Z UID:0000000460@events.thp.uni-koeln.de DESCRIPTION:Roderick MacKenzie\, Nottingham University\n\nSimulating organ ic electrons - from fullerenes to whole devices\n\n\n\nContact Person: Pau l H.M. van Loosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Yoshio Kuramoto DTSTART;TZID=Europe/Berlin:20140314T140000 DTEND;TZID=Europe/Berlin:20140314T153000 DTSTAMP:20260527T090435Z UID:0000000462@events.thp.uni-koeln.de DESCRIPTION:Yoshio Kuramoto\, Tohoku University\n\nSuperconductivity and m ultipoles of electron-spin composites in two-channel Kondo lattice\n\nThe Kondo lattice model\, if properly generalized\, provides microscopic under standing of rich varieties of ordering phenomena in strongly correlated el ectrons. Moreover\, the model can predict new orders that can be tested e xperimentally. We demonstrate novel electronic orders in the Kondo lattic e by including multi-bands of conduction electrons. The resultant two-cha nnel Kondo lattice at zero temperature cannot remain disordered because of the remaining fractional entropy at each site\, and unconventional orders are realized. The hidden symmetry SO(5) of the model at half-filling of c onduction bands causes degeneracy between multipole composite orders with three components\, and an odd-frequency superconducting order with a compl ex order parameter. Detailed numerical calculation shows that deviation f rom the half-filling makes the superconductivity most stable for a certain range of the density. We discuss peculiar features of the order paramet ers.\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Bernard Kippelen DTSTART;TZID=Europe/Berlin:20140320T100000 DTEND;TZID=Europe/Berlin:20140320T113000 DTSTAMP:20260527T090435Z UID:0000000466@events.thp.uni-koeln.de DESCRIPTION:Bernard Kippelen\, Georgia Institute of Technology\n\nAdvances in Organic Flexible Optolectronics\n\n\n\nContact Person: Klaus Meerholz LOCATION:Seminarraum 147\, Institut für Physikalische Chemie END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Xenophon Zotos DTSTART;TZID=Europe/Berlin:20140328T140000 DTEND;TZID=Europe/Berlin:20140328T153000 DTSTAMP:20260527T090435Z UID:0000000467@events.thp.uni-koeln.de DESCRIPTION:Xenophon Zotos\, University of Crete\n\nSome new insights in 1 D quantum magnets\n\n\n\nContact Person: Paul H.M. van Loosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Rüegg DTSTART;TZID=Europe/Berlin:20140416T143000 DTEND;TZID=Europe/Berlin:20140416T160000 DTSTAMP:20260527T090435Z UID:0000000448@events.thp.uni-koeln.de DESCRIPTION:Christian Rüegg\, Paul Scherrer Institute\, University of Gen eva\n\nQuantum Phase Transitions in Model Magnets\n\nSome magnets are exce ptional solid-state model systems for high-precision studies of fundamenta l quantum phenomena in physics like Bose-Einstein condensates and Tomonaga -Luttinger liquids [1\,2]. Further examples include complex ground states and correlations realized in low-dimensional and frustrated systems [3\,4] \, exciting physics of impurities and quenched disorder [5]\, and dramatic events near quantum phase transitions [6]. In this colloquium studies of model oxides and halides by neutron scattering and complementary experimen tal techniques will be presented. Classical phase transitions in such comp ounds can be controlled easily by temperature\, interactions and quantum f luctuations by chemistry and pressure application\, and correlations and p article numbers by magnetic field. The experimental results will be discus sed in the context of recent developments of powerful computational method s enabling fully quantitative analysis and of related work on other model systems like gases of ultracold atoms.\n[1] T. Giamarchi et al.\, Nature P hysics 4\, 198 (2008).\n[2] B. Thielemann et al.\, Phys. Rev. Lett. 102\, 107204 (2009).\n[3] Y. Kohama et al.\, Phys. Rev. Lett. 109\, 167204 (2012 ).\n[4] F. Casola et al.\, Phys. Rev. Lett. 110\, 187201 (2013).\n[5] S. W ard et al.\, J. Phys.: Condens. Matter 25\, 014004 (2013).\n[6] P. Merchan t et al.\, Nature Physics\, in press (2014).\n\n\nContact Person: Simon Tr ebst LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Daniel Grumiller DTSTART;TZID=Europe/Berlin:20140507T141500 DTEND;TZID=Europe/Berlin:20140507T160000 DTSTAMP:20260527T090435Z UID:0000000477@events.thp.uni-koeln.de DESCRIPTION:Daniel Grumiller\, Vienna University of Technology\n\nHolograp hy: From (flat space) gravity to quantum matter\n\nThe description of stro ngly coupled systems presents a challenge for theoretical physics\, since usual weak-coupling methods based upon perturbation theory typically fail. Therefore\, new tools are required to describe strongly interacting quant um matter\, like the quark gluon plasma created in heavy ion collisions or cold fermionic atoms at unitarity. Holographic correspondences between gr avity theories and quantum field theories can provide such tools. I review basic aspects of holography and summarize our recent results in flat spac e holography\n\nContact Person: Thomas Nattermann LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Alpha N'Diaye DTSTART;TZID=Europe/Berlin:20140514T143000 DTEND;TZID=Europe/Berlin:20140514T160000 DTSTAMP:20260527T090435Z UID:0000000447@events.thp.uni-koeln.de DESCRIPTION:Alpha N'Diaye\, Lawrence Berkeley National Laboratory\n\nTunin g chirality in magnetic thin films through interface engineering\n\n\n\nCo ntact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Frank Ferrari DTSTART;TZID=Europe/Berlin:20140521T143000 DTEND;TZID=Europe/Berlin:20140521T160000 DTSTAMP:20260527T090435Z UID:0000000458@events.thp.uni-koeln.de DESCRIPTION:Frank Ferrari\, Université libre de Bruxelles\n\nOn Quantum B lack Holes\n\n\n\nContact Person: Semyon Klevtsov LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Heiko Wende DTSTART;TZID=Europe/Berlin:20140528T143000 DTEND;TZID=Europe/Berlin:20140528T160000 DTSTAMP:20260527T090435Z UID:0000000468@events.thp.uni-koeln.de DESCRIPTION:Heiko Wende\, University of Essen-Duisburg\n\nMagnetic Hybrid Systems: from Molecules and Graphene to Multiferroic Nanocomposites\n\nIn the on-going process of electronic device miniaturization new concepts are developed by utilizing hybrid systems. For this purpose the tailoring of the magnetic properties in these nanoscale systems is essential. We make u se of hybrid systems that consist of a combination of magnetic molecules\, graphene\, thin films as well as magnetic nanopillars. Surface and interf ace effects are crucial to achieve new functionalities in these structures . This shall be demonstrated by means of two examples: 1) The magnetic cou pling of paramagnetic molecules to ferromagnetic surfaces can be tailored by the help of an intermediate layer of atomic oxygen or graphene [1-4]. T he fundamental understanding of the relevant interactions for the coupling is possible by combination of experimental and theoretical results utiliz ing ab initio calculations. 2) Ferrimagnetic CoFe2O4 (CFO) nanopillars emb edded in a ferroelectric BaTiO3 (BTO) matrix are an example for a two-phas e magnetoelectrically coupled system [5]. In particular\, the\n \n [1] H. Wende et al.\, Substrate-induced magnetic ordering and switching of iron porphyrin molecules\, Nature Materials 6\, 516 (2007).\n [2] H. Wende\, Molecular magnets: How a nightmare turn s into a vision\, \nNature Materials 8\, 165 (2009).\n [3] M. Bernien et al.\, Tailoring the Nature of Magnetic Coupling of Fe-Po rphyrin Molecules to Ferromagnetic Substrates\, Phys. Rev. Lett. 102\, 047 202 (2009).\n [4] S. Bhandary et al.\, Graphene as a Re versible Spin Manipulator of Molecular Magnets\, Phys. Rev. Lett. 107\, 25 7202 (2011).\n [5] C. Schmitz-Antoniak et al.\, Electri c in-plane polarization in multiferroic CoFe2O4/BaTiO3 nanocomposite tuned by magnetic fields\, Nature Communications 4:2051 doi: 10.1038/ncomms3051 (2013).\n\n\nContact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Claudio Castelnovo DTSTART;TZID=Europe/Berlin:20140604T143000 DTEND;TZID=Europe/Berlin:20140604T160000 DTSTAMP:20260527T090435Z UID:0000000456@events.thp.uni-koeln.de DESCRIPTION:Claudio Castelnovo\, University of Cambridge\n\nDynamics of fr actionalised excitations in spin ice materials\n\nSpin ice materials such as Dy2Ti2O7 and Ho2Ti2O7 provide a rare instance of emergent gauge symmetr y and fractionalisation in three dimensions. Their elementary excitations carry a fraction of the magnetic moment of the microscopic spin degrees of freedom and they can be thought of as magnetic monopoles. Spin ice ground states are highly degenerate yet locally constrained and in the absence o f monopole excitations\, effectively no dynamics is possible. At low tempe ratures\, the monopoles are sparse and dynamics becomes very slow. These s ystems are therefore prone to falling out of equilibrium at low temperatur es\, for instance following comparatively rapid changes in temperature or applied magnetic field. In this regime\, a wealth of dynamical phenomena o ccur\, including reaction diffusion behaviour\, slow dynamics due to kinem atic constraints\, as well as behaviour that mimic the deposition of inter acting dimers on a lattice. The situation is further complicated by the pr esence of disorder that\, even at small\n densities\, appears to have a si zeable effect on the low-temperature dynamics of these systems. Here we in vestigate some of these phenomena and we propose how to effectively extend existing theories to describe spin ice out of equilibrium. Nonequilibrium physics in spin ice is a novel setting which combines kinematic constrain ts\, emergent topological defects\, and magnetic long range Coulomb intera ctions. \n\n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Viktor Zolyomi DTSTART;TZID=Europe/Berlin:20140611T143000 DTEND;TZID=Europe/Berlin:20140611T160000 DTSTAMP:20260527T090435Z UID:0000000475@events.thp.uni-koeln.de DESCRIPTION:Viktor Zolyomi\, Lancaster University\n\nBeyond Graphene: The future of two-dimensional nanomaterials\n\nNanoscale materials science has been dominated by graphene for the past ten\nyears. The presentation will discuss the way forward by looking at a number of\nemerging novel materia ls that are expected to define the next decade of\nresearch in two-dimensi onal materials. The presentation will focus on two\nclasses of semiconduc ting nanomaterials: hexagonal chalcogenides and\nsilicene/germanene deriva tives.\n\nHexagonal gallium chalcogenides and indium chalcogenides are str ucturally\nquite similar to transition metal dichalcogenides while exhibit ing very unique\nelectronic properties. Their valence band will be discuss ed with emphasis on\ntheir use to engineer a very robust Lifshitz transiti on\, and their optical\nproperties will be examined to project their futur e use as UV photodetectors\n[1\,2\,3].\n\nSilicane and germanane are fully hydrogenated covalent derivatives of silicene\nand germanene\, respective ly. Their stability will be discussed and their\nelectronic structure pres ented. The talk will show that a tight-binding\ndescription of their valen ce and conduction bands requires the inclusion of\nsecond-nearest neighbor interaction and present a model with parameters\nobtained from first prin ciples [4\,5].\n\n\n[1] Zólyomi\, V.\; Drummond\, N. D.\; Fal'ko\, V. I.\ ; Phys. Rev. B 87\, 195403\n(2013)\n\n[2] Liu\, F. C.\; Shimotani\, H.\; S hang\, H.\; Kanagasekaran\, T.\; Zólyomi\, V.\;\nDrummond\, N. D.\; Fal'k o\, V. I.\; Tanigaki\, K.\; ACS Nano 8\, 752-760 (2014)\n\n[3] Zólyomi\, V.\; Drummond\, N. D.\; Fal'ko\, V. I.\; arXiv:1403.4389\n\n[4] Drummond\, N. D.\; Zólyomi\, V.\; Fal'ko\, V. I.\; Phys. Rev. B 85\, 075423\n(2012) \n\n[5] Zólyomi\, V.\; Wallbank\, J. R.\; Fal'ko\, V. I.\; 2D Mater. 1\, 011005 (2014)\n\n\nContact Person: Alexander Grueneis LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Heß DTSTART;TZID=Europe/Berlin:20140618T143000 DTEND;TZID=Europe/Berlin:20140618T160000 DTSTAMP:20260527T090435Z UID:0000000455@events.thp.uni-koeln.de DESCRIPTION:Christian Heß\, IFW Dresden\n\nUnconventional superconductivi ty in LiFeAs as seen by scanning tunneling microscopy and spectroscopy\n\n In this talk\, I will present recent results on the unconventional superco nductor LiFeAs obtained by scanning tunneling micrsopcopy/spectroscopy (S TM/STS). STM. STM/STS is an important probe for studying such superconduct ors. On the one hand it provides the possibility to directly measure the s patial variation of the order parameter in the presence of a magnetic vort ex lattice\, and thus the coherence length. On the other hand\, the quasip article interference (QPI) which arises from quasiparticle scattering off impurities\, and which sensitively depends on the superconducting wave fun ction can be probed directly. LiFeAs belongs to the class of iron arsenide superconductors which have been discovered in 2008. This material possess es very clean and charge neutral cleaved surfaces without a surface state and is thus perfectly suited for STM/STS. Our QPI data are perfectly cons istent with band structure data derived from angular reolved photoemission spectroscopy [1].\nHowever\, the further analysis yields incompatibility with elementary s- or d-wave order parameters\, suggestive of a more compl ex scenario [2]. I will discuss these findings in the context of further e xperimental data and theoretical results.\n\n[1] C. Hess\, S. Sykora\, T. Hänke\, R. Schlegel\, D. Baumann\, V. B. Zabolotnyy\, L. Harnagea\, S. Wu r­mehl\, J. van den Brink\, B. Büchner\, Phys. Rev. Lett. 110\, 017006 ( 2013)\n[2] T. Hänke\, S. Sykora\, R. Schlegel\, D. Baumann\, L. Harnagea\ , S. Wurmehl\, M. Daghofer\, B. Büch­ner\, J. van den Brink\, C. Hess\, Phys. Rev. Lett. 108\, 127001 (2012) \n\n\nContact Person: Paul H.M. van L oosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Gianni Profeta DTSTART;TZID=Europe/Berlin:20140626T160000 DTEND;TZID=Europe/Berlin:20140626T173000 DTSTAMP:20260527T090435Z UID:0000000476@events.thp.uni-koeln.de DESCRIPTION:Gianni Profeta\, CNR-SPIN and University of L'Aquila\n\nPhysic al properties of superconductors from Density Functional Theory\n\nThe rec ent discovery of superconductivity at high temperature in\niron-based mate rials have highly\nrenewed the interest in the scientific community for th e comprehension of\nthe physical properties of\nsuperconductors and their applications.\nIn this talks\, we will give an overview of some new experi mental results\nin this field and their theoretical interpretations\nby me ans of density functional theory calculations.\nIn particular\, we will pr esent results on the effects of charge doping\,\npressure and reduced dime nsionality on the electronic\,\nFermi surface topology and magnetic proper ties in conventional and\nnon-conventional superconductors\,\nhighlighting their debated role in the appearance of the superconducting\nphase.\n\n\n Contact Person: Alexander Grueneis LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Bum Joon Kim DTSTART;TZID=Europe/Berlin:20140702T143000 DTEND;TZID=Europe/Berlin:20140702T160000 DTSTAMP:20260527T090435Z UID:0000000459@events.thp.uni-koeln.de DESCRIPTION:Bum Joon Kim\, MPI FKF Stuttgart\n\nThe quest for novel high-t emperature superconductors\n\nAfter nearly three decades of research on hi gh temperature superconductivity\, the transition temperature remains stag nant and our understanding incomplete. In this talk\, I will argue that fi nding a novel material system that mimics the cuprate physics can provide a breakthrough. Ruddelsden-popper series iridates display remarkable simil arity to high-Tc cuprates in terms of crystal\, lattice\, and magnetic str uctures\, which lead to similarity in the effective low-energy physics as manifested by the unique cuprate fermiology reproduced in Sr2IrO4. How sup erconductivity emerges or fails in this new class of materials will reveal essential features of high temperature superconductivity\; in particular the long-sought connection between the pseudogap and superconductivity.\n\ nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christoph Tegenkamp DTSTART;TZID=Europe/Berlin:20140709T143000 DTEND;TZID=Europe/Berlin:20140709T160000 DTSTAMP:20260527T090435Z UID:0000000469@events.thp.uni-koeln.de DESCRIPTION:Christoph Tegenkamp\, Universität Hannover\n\n“Edge science ”: electronic states in geometrically and electronically confined surfa ce structures\n\nFascinating phenomena such as superconductivity\, charge density waves\, Luttinger liquids or topologically protected edge states\, can be realized on surfaces with atomic precision. Strongest correlation effects are expected in 1D structures and I will present in this talk two recent examples of geometrically and electronically confined systems fabri cated by lithography and self-assembly\, respectively\, where the spectros copic signatures and transport properties are determined by their edges an d step structures: \nPb adsorbed on Si(557) leads to formation of long ra nge ordered quantum wire ensembles. At temperatures below 78K the system u ndergoes a refacetting transition accompanied by a metal-insulator transit ion. The insulating behavior found in the direction across the wires can b e explained in terms of Fermi nesting [1]. Recently\, the spin-orbit coupl ing in this system and its impact to magneto-transport measurements have b een analyzed in detail. The spin polarization of the Fermi surface\, manif ested already in the suppression of spin-orbit coupling along the wires wi thin the 1D transport regime\, has been confirmed by spin-resolved ARPES m easurements. The magnitude of the Rashba-splitting in this strongly anisot ropic system evidences the formation of a spin density wave\, which is the ground state of a CDW system electron-electron interaction [2]. \nThe reg ime of mesoscopic transport physics has been entered with graphene nanorib bon structures (GNR) grown on SiC-MESAs. By means of a 4-tip STM/SEM syste m ballistic transport channels with mean free path lengths up to 10 µm at room temperature have been identified [3]. The existence of edge-localize d states near the zig-zag edges have been confirmed by first STS spectra t aken across the ribbon [4]. \n[1] C. Tegenkamp\, et.al. PRL 95\, 176804 (2 005)\n[2] C. Tegenkamp\, et.al. PRL 109\, 266401 (2012) \n[3] J. Baringhau s \,et.al.\, Nature 506\, 349 (2014)\n[4] J. Baringhaus et.al. JPCM\, 25\ , 392001 (2013).\n\nContact Person: Carsten Busse LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Eran Sela DTSTART;TZID=Europe/Berlin:20140716T143000 DTEND;TZID=Europe/Berlin:20140716T160000 DTSTAMP:20260527T090435Z UID:0000000501@events.thp.uni-koeln.de DESCRIPTION:Eran Sela\, University of Tel Aviv\n\nFractional helical liqui ds in quantum wires\n\n\nIn this talk I will argue that the physics of the fractional quantum Hall effect my arise\, under certain conditions and li mitations\, directly in one dimensional systems. \n\nThe primary example t hat will be discussed is that of one dimensional wires with spin-orbit cou pling. We will show that in the presence of Zeeman fi eld and strong elect ron-electron interaction\, a clean wire may form fractional helical liquid \nstates with phenomenology similar to fractional quantum Hall liquids. Mo st notably\, the wire's\ntwo terminal conductance is predicted to show fra ctional quantized conductance plateaus at low\nelectron density. The eleme ntary charge excitation of the wire is fractional and affects the shot noi se in a nontrivial way. When the system is proximity-coupled to a superco nductor\, fractional Majorana\nbound states may be stabilized\, giving ris e to 1D analog of non-abelian anyons. I will discuss how\ndisorder destabi lizes these fractional phases. Possible numerical checks of the predicted effects will be discussed.\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Paul Wiegmann DTSTART;TZID=Europe/Berlin:20140723T143000 DTEND;TZID=Europe/Berlin:20140723T160000 DTSTAMP:20260527T090435Z UID:0000000481@events.thp.uni-koeln.de DESCRIPTION:Paul Wiegmann\, University of Chicago\n\nt.b.a.\n\n\n\nContact Person: Seymon Klevtsov LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Teichert DTSTART;TZID=Europe/Berlin:20140827T143000 DTEND;TZID=Europe/Berlin:20140827T160000 DTSTAMP:20260527T090435Z UID:0000000502@events.thp.uni-koeln.de DESCRIPTION:Christian Teichert\, Montanuniversität Loeben\, Austria\n\nOr ganic thin film growth on graphene\n\nCrystalline films of small organic s emiconductors offer attractive potential for electronic and optoelectronic applications. To realize such applications on flexible substrates\, graph ene as a transparent electrode material comes into play. We studied the g rowth of the rod-like oligophenylene molecule para-hexaphenyl (6P) on meta l supported as well as on exfoliated graphene. On clean graphene\, the mol ecules grow in a lying fashion on the substrate whereas contaminations cau se the molecules to stand up. Islands of upright 6P molecules are also obs erved on ion-bombarded surfaces. We found recently that on ion bombarded r utile(110) under oblique incidence the resulting nanometer surface ripples significantly change the shape of the 6P islands.\n\nContact Person: Thom as Michely LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Gregor Mussler DTSTART;TZID=Europe/Berlin:20140903T143000 DTEND;TZID=Europe/Berlin:20140903T160000 DTSTAMP:20260527T090435Z UID:0000000510@events.thp.uni-koeln.de DESCRIPTION:Gregor Mussler\, FZ Jülich\n\nt.b.a.\n\n\n\nContact Person: M arkus Grüninger LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Teichert DTSTART;TZID=Europe/Berlin:20140911T130000 DTEND;TZID=Europe/Berlin:20140911T170000 DTSTAMP:20260527T090435Z UID:0000000516@events.thp.uni-koeln.de DESCRIPTION:Christian Teichert\, Montanuniversität Leoben\n\nAFM Tutorial : Nanostructure Characterization by Atomic Force Microscopy\n\n\n\nContact Person: not specified LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Teichert DTSTART;TZID=Europe/Berlin:20140912T130000 DTEND;TZID=Europe/Berlin:20140912T170000 DTSTAMP:20260527T090435Z UID:0000000517@events.thp.uni-koeln.de DESCRIPTION:Christian Teichert\, Montanuniversität Leoben\n\nAFM Tutorial : Nanostructure Characterization by Atomic Force Microscopy\n\n\n\nContact Person: not specified LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Charles Reichhardt DTSTART;TZID=Europe/Berlin:20140922T140000 DTEND;TZID=Europe/Berlin:20140922T153000 DTSTAMP:20260527T090435Z UID:0000000545@events.thp.uni-koeln.de DESCRIPTION:Charles Reichhardt\, Los Alamos\n\nSkyrmion Lattices in Random and Ordered Potential Landscapes\n\nSince the initial discovery of skyrmi on lattices in chiral magnets [1]\, there has been a tremendous growth in this field as an increasing number of compounds are found to have extended regions of stable skyrmion lattices [2] even close to room temperature [3 ]. These systems have significant promise for applications due to their s ize scale and the low currents or drives needed to move the skyrmions [4]. Another interesting aspect of skyrmions is that the equations of motion have significant non-dissipative terms or a Magnus effect which makes them unique in terms of collective driven dynamics as compared to other system s such as vortex lattices in type-II superconductors\, sliding charge dens ity waves\, and frictional systems. We examine the driven dynamics of sky rmions interacting with random and periodic substrate potentials using bot h continuum based modelling and particle based simulations. In clean syste ms we examine the range in which skyrmion motion can be explored as a func tion of the magnetic field and current and show that there can be a curren t-induced creation or destruction of skyrmions. In systems with random pi nning we find that there is a finite depinning threshold and that the Hall angle shows a strong dependence on the disorder strength. We also show th at features in the transport curves correlate with different types of skyr mion flow regimes including a skyrmion glass depining/skyrmion plastic flo w region as well as a transition to a dynamically reordered skyrmion cryst al at higher drives. We find that increasing the Magnus term produces a lo w depinning threshold which is due to a combination of skyrmions forming c omplex orbits within the pinning sites and skyrmion-skyrmion scattering e ffects. If the skyrmions are moving over a periodic substrate\, with incr easing drive the Hall angle changes in quantized steps which correspond to periodic trajectories of the skyrmion that lock to symmetry directions of the substrate potential.\n\n[1] S. Muhlbauer et al Science 323 915 (2009) .\n[2] X. Z. Yu et al. Nature 465\, 901–904 (2010). \n[3] X.Z. Yu et al Nature Materials\, 10\, 106 (2011).\n[4] A. Fert\, V. Cros\, and J. Sampa io Nature Nanotechnology 8\, 152 (2013).\n\n\nContact Person: Markus Garst LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Igor Shavrin DTSTART;TZID=Europe/Berlin:20140923T100000 DTEND;TZID=Europe/Berlin:20140923T113000 DTSTAMP:20260527T090435Z UID:0000000544@events.thp.uni-koeln.de DESCRIPTION:Igor Shavrin\, Aalto University\n\nApplications of photonic cr ystal fiber in high-resolution interferometry\n\nIn this talk I will prese nt my research in supercontinuum light generation in photonic crystal fibe rs (PCF) and describe two applications of these fibers in high resolution interferometry. In one application PCF is utilized in a light source for h igh resolution stroboscopic white-light interferometry\, the technique use d for characterization of surface acoustic vibrations. Another application uses hollow-core PCF as a waveguide and gas cell for simultaneous measure ment of the complex refractive index in gaseous analytes. \n\nContact Pers on: Klas Lindfors LOCATION:Institute of Chemistry\, PC302 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Fulvio Parmigiani DTSTART;TZID=Europe/Berlin:20141008T143000 DTEND;TZID=Europe/Berlin:20141008T160000 DTSTAMP:20260527T090435Z UID:0000000457@events.thp.uni-koeln.de DESCRIPTION:Fulvio Parmigiani\, University of Trieste\n\nSpin and time res olved photoelectron spectroscopy in the momentum space of archetypal topol ogical insulators\n\nThe interaction between light and the topologically p rotected spin polarized Dirac particles at the surface of topological insu lators (TIs) constitutes the key issue for the development of opto-spintro nics devices. Laser-based time and angle resolved photoelectron spectrosco py (tr-ARPES) in the sub-ps time domain represents an important experiment al tool to investigate the ultrafast light-induced modification of the ele ctronic properties in TIs. Several studies recently disclosed a very rich scenario\, characterized by long-lived electronic population [ref. Sobota] \, Floquet-Bloch states [ref. Gedik science]\, reduction of the electron-p honon coupling [ref Crepaldi2] and the possibility to tune the Schottky ba rrier [ref. Marsi]. Despite the large number of experimental investigation s of the out-of-equilibrium electronic properties [ref. Sobota JP\, Chulko v\, Perfetti\, Crepaldi1]\, a detailed description of the microscopic scat tering mechanisms within the surface state and between the bulk conduction band and the surface state is lacking\, so far. Here an overview of the m ost recent discoveries relevant to the evolution of the electron populatio n optically-injected in the topologically protected state at the surface i s reported. In particular\, we prove that only by measuring the spin-inten sity signal over several orders of magnitude in spin- time- and angle reso lved photoemission spectroscopy (s-tr-ARPES) experiments it is possible to comprehensively describe the optically excited electronic states in TIs m aterials. Remarkably\, the experimental data\, interpreted on the base of ab-initio fully relativistic spin resolved photoemission calculations and spin dynamics modeling\, unambiguously show that two non-interacting elect ronic systems\, derived from the excited surface and bulk states\, are cha racterizing the non-equilibrium electronic properties of the archetypal TI \, Bi2Se3.\n\nContact Person: Paul H.M. van Loosdrecht LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Denis Vyalikh DTSTART;TZID=Europe/Berlin:20141015T143000 DTEND;TZID=Europe/Berlin:20141015T160000 DTSTAMP:20260527T090435Z UID:0000000514@events.thp.uni-koeln.de DESCRIPTION:Denis Vyalikh\, Institute of Solid State Physics\, University of Technology Dresden\, D-01062 Dresden\, Germany\n\nARPES insight into th e properties of f-electrons in rare-earth intremetallics\n\nFor a long tim e\, rare-earth (RE) intermetallic materials have attracted considerable in terest be-cause of their exotic properties at low temperatures which inclu de complex magnetic phases\, valence fluctuations\, heavy-fermion states\, Kondo behavior and many others. It is widely believed that all of these p roperties stem from the delicate interplay between almost localized 4f ele ctrons and itinerant valence band states.\nOur experiments aim to disclose details of this interaction\, and reveal the fine electronic struc-ture o f such materials near the Fermi level. To this end\, we apply Angle-Resolv ed Photoemission Spectroscopy (ARPES) technique\, which in spite of its su rface sensitivity when working in UV mode\, indeed\, allows to gain deep i nsight not only into surface electron structure\, but to probe the bulk de -rived states\, too. In that regard\, the particular point of our experime nts is the proper discrimination of (sub-) surface and bulk related phenom ena. \nIn the past years we performed extensive ARPES studies on the RERh2 Si2 (RE = Ce\, Eu and Yb) series of compound as well as on YbIr2Si2 With o ur approach we were able to address some of the topics at the core of stro ngly correlated 4f electron systems: (i) observation of crystal-electric f ield (CEF) splitting of the 4f states and their fine dispersion induced by f-d hybridization\; (ii) insight into the Fermi surface and manifestation of its strong 4f character. Disclosing its topology and features reflecti ng f-d coupling at the surface and bulk of the material. Studying its temp erature dependence for a Kondo lattice (YbRh2Si2)\; (iii) clear evidence o f the interplay of Dirac fermions and heavy quasi-particles\; (iv) manifes tation of unusual and strong ferromagnetism at the Si-terminated surface o f an antiferromagnet (EuRh2Si2) caused by buried 4f magnetic moments of Eu lying 4-layers below the surface.\n\n[1] A. Chikina et al.\, Strong ferro magnetism at the surface of an antiferromagnet caused by buried magnetic m oments\, Nature Communications 5\, 3171 (2014).\n\n[2] M. Höppner et al.\ , Interplay of Dirac fermions and heavy quasiparticles in solids\, Nature Commu-nications 4\, 1646 (2013).\n\n[3] S. Danzenbächer et al.\, Insight into the f-derived Fermi surface of the heavy-fermion compound YbRh2Si2\, Phys. Rev. Lett. 107\, 267601 (2011).\n\n[4] D.V. Vyalikh et al.\, k-depen dence of the crystal-field splittings of 4f states in rare-earth systems\, Phys. Rev. Lett. 105\, 237601 (2010).\n\n[5] D.V. Vyalikh et al.\, Tuning the hybridization at the surface of a heavy-fermion system\,\nPhys. Rev. Lett.\, 103\, 137601 (2009).\n\n\nContact Person: Alexander Grueneis LOCATION:Seminar Room of the Institute of Physics II (R201) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Karl Leo DTSTART;TZID=Europe/Berlin:20141028T140000 DTEND;TZID=Europe/Berlin:20141028T153000 DTSTAMP:20260527T090435Z UID:0000000322@events.thp.uni-koeln.de DESCRIPTION:Karl Leo\, TU Dresden\n\nRecent progress in organic light-emit ting diodes and solar cells\n\n\n\nContact Person: Achim Rosch LOCATION:HS 2\, Institute of Chemistry END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Fulvio Parmigiani DTSTART;TZID=Europe/Berlin:20141104T160000 DTEND;TZID=Europe/Berlin:20141104T173000 DTSTAMP:20260527T090435Z UID:0000000566@events.thp.uni-koeln.de DESCRIPTION:Fulvio Parmigiani\, University of Trieste\n\nScience driven re quirements for seeded soft X-ray free electron lasers\n\nStarting from the archetypal FERMI externally seeded FEL\, recent theoretical and experimen tal progress has shown the possibility of producing fully coherent\, varia ble polarization and tunable\, soft-X-ray\, ultra-short pulses at high rep etition rate. \n\nThis ultimate achievement will unlock the gate for perfo rming X-ray-based experiments that are qualitatively different from those available at any current or planned X-ray source.\n\nHere we will review t he experiments and the ideas that represent the science frontier in soft X -ray\, time-resolved spectroscopy\, coherent imaging and scattering experi ments.\n\nThese studies will lead to an understanding of fundamental dynam ics\, occurring on the ultrafast time and nanometer spatial scales\, neede d for addressing a broad range of science essential for resolving our comp lex and long-term energy challenges\, environmentally urgent questions and demanding problems in bioscience and novel materials. \n\nContact Person : Paul H.M. van Loosdrecht LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Elisabeth Sörgel DTSTART;TZID=Europe/Berlin:20141112T143000 DTEND;TZID=Europe/Berlin:20141112T160000 DTSTAMP:20260527T090435Z UID:0000000518@events.thp.uni-koeln.de DESCRIPTION:Elisabeth Sörgel\, Universität Bonn\n\nExploiting the capabi lities of scanning probe microscopy for the investigation of ferroelectri cs\n\nFerroelectrics exhibit a spontaneous dipole moment whose orientation can be determined by the application of electric fields. This allows for the controlled fabrication of ferroelectric domain patterns which are\, fo r instance\, in use for efficient frequency doubling using quasi phase mat ching. Although known since more than fifty years\, and intensively invest igated for applications\, lots of basic knowledge and understanding of fer roelectrics is still missing. \nTo start with\, I will briefly introduce f erroelectrics as a material itself\, and in particular show the potential of domain-structured ferroelectrics. In the main part of my talk I will di scuss the possibilities of scanning probe microscopy (SFM) for a better un derstanding of ferroelectrics and also ferroelectric domains. Finally\, I will present our results on structuring lithium niobate surfaces. \n\n\nCo ntact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Ionela Vrejoiu DTSTART;TZID=Europe/Berlin:20141119T143000 DTEND;TZID=Europe/Berlin:20141119T160000 DTSTAMP:20260527T090435Z UID:0000000567@events.thp.uni-koeln.de DESCRIPTION:Ionela Vrejoiu\, MPI for Solid State Research\, Stuttgart\n\nC hallenges and driving forces for interfacing functional perovskite oxides \n\nThe large spectrum of perovskite oxides provides virtually unlimited p ossibilities to design and fabricate interfaces with functional properties . The ability to produce clean and sharp interfaces between oxide material s in a controlled manner provides appealing possibilities to generate nove l electronic phases. Crucial steps in achieving high quality epitaxial oxi de heterostructures have been the use of pulsed-laser deposition and molec ular-beam epitaxy for the growth of multicomponent oxides\, the ability to terminate oxide substrates at well-defined ionic planes\, and the develop ment of high pressure reflection high-energy electron diffraction to monit or the deposition of individual atomic layers. In consequence now epitaxia l perovskite heterostructures can be fabricated with atomic-layer precisio n. In my presentati on I will show examples of physical properties of epitaxial oxide heterost ructures I have fabricated by pulsed-laser deposition. The emphasis will b e on justifying the choice of the perovskite oxides that were interfaced ( ferromagnetic manganites and ruthenates and ferroelectrics) and on the rol e of the interfaces\, and their quality\, in establishing the physical pro perties of these particular heterostructures. \n\nContact Person: Markus G rüninger LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Oliver Rader DTSTART;TZID=Europe/Berlin:20141126T143000 DTEND;TZID=Europe/Berlin:20141126T160000 DTSTAMP:20260527T090435Z UID:0000000547@events.thp.uni-koeln.de DESCRIPTION:Oliver Rader\, Helmholtz-Zentrum Berlin\n\nExperiments on band gap opening and spin manipulation in graphene and toplogical insulators \ n\nGraphene as two-dimensional conductor and topologial insulators which p ossess two-dimensional metallic surface states around an insulating volume share also quasirelativistic properties of their charge carriers. Their c haracteristic linear E(k) band dispersions can be observed as so-called Di rac cones in angle-resolved photoelectron spectroscopy. In graphene\, they are caused by pseudospin properties\, in topological insulators such as B i2Se3 by the electron spin. This opens the possibility to manipulate trans port properties by opening a surface band gap at the Dirac crossing point through breaking of the sublattice symmetry of graphene or the time-revers al symmetry of topological insulators. In the talk\, examples are shown wh ere these attempts lead to surprising results. In a further step\, graphen e is made spin dependent by an extrinsic spin orbit interaction. The resul ting spin polarization is in the surface plane - the same is the case with topological insulators. The opening of the Dirac point by symmetry breaki ng should in both cases turn the spin perpendicular to the surface. This i s demonstrated for graphene. For topological insulators\, we show that the spin can be turned out of the plane by polarized light in the photoemissi on process.\n\nContact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Ivan Bihuega DTSTART;TZID=Europe/Berlin:20141210T143000 DTEND;TZID=Europe/Berlin:20141210T160000 DTSTAMP:20260527T090435Z UID:0000000573@events.thp.uni-koeln.de DESCRIPTION:Ivan Bihuega\, Universidad Autonoma de Madrid\n\nVisualizing a nd manipulating graphene physics at the atomic scale\n\nIn 2004 graphene c eased being a theoretical chimera to become the object of desire of the sc ientific community. In just few years\, extraordinary properties have bein g demonstrated and many others are emerging as a result of the tremendous experimental and theoretical efforts devoted to this material. In this tal k I will show how we use a scanning tunneling microscope to explore and ma nipulate graphene physics at an atomic level. I will mainly concentrate in two topics:\n-The investigation\, at the atomic scale\, of the impact tha t point defects like vacancies or atomic H have in the structural\, electr onic and magnetic properties of graphene layers grown on different substra tes\, where the pure bidimensionality of graphene gives to these atomic de fects a critical role.\n-The study of the coupling of graphene with its lo cal environment and how this affects to graphene’s quasiparticle dispers ion\, pseudospin\, van Hove singularities...\, which is absolutely critica l to be able to integrate it in tomorrow's electronic devices. \n\n\nConta ct Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Arkady V. Krasheninnikov DTSTART;TZID=Europe/Berlin:20150113T140000 DTEND;TZID=Europe/Berlin:20150113T160000 DTSTAMP:20260527T090435Z UID:0000000614@events.thp.uni-koeln.de DESCRIPTION:Arkady V. Krasheninnikov\, Aalto University\, Finland \n\nLect ure on 2D Transition-Metal Dichalcogenides: Doping\, Alloying and Electron ic Structure Engineering \n\nFollowing isolation of a single sheet of grap hene\, many other 2D systems were manufactured. Among them\, single transi tion metal dichalcogenides (TMD) sheets have received a particular attenti on\, as these materials exhibit intriguing electronic\, optical and mechan ical properties which can be controlled by varying material composition. M oreover\, the properties can further be tuned by introduction of defects a nd impurities. \nIn this lecture\, after a brief introduction to the struc ture and properties of TMDs\, I will present the results of our first-pri nciples theoretical studies of the morphology\, electronic and optical pro perties of 2D TMDs obtained in collaboration with several experimental gro ups. I will further discuss how defects and impurities can be used to tune the characteristics of 2D TMDs. I will also touch upon the stability and electronic characteristics of mixed TMDs\, such as MoS2xSe2(1−x)\, which can be referred to as 2D random alloys. We demonstrated that 2D mixed ter nary MoS2/MoSe2/MoTe2 compounds are thermodynamically stable at room tempe rature\, and that the gap in such systems is direct and can continuously b e tuned\, as confirmed now by the experiments carried out by several group s. \n\n\nContact Person: Thomas Michely LOCATION:Seminar room 03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Andriy Shevchenko DTSTART;TZID=Europe/Berlin:20150114T143000 DTEND;TZID=Europe/Berlin:20150114T160000 DTSTAMP:20260527T090435Z UID:0000000588@events.thp.uni-koeln.de DESCRIPTION:Andriy Shevchenko\, Aalto Universität\n\nSpatially dispersive optical metamaterials: Design and applications\n\nThe presentation concer ns spatially dispersive optical metamaterials\, for which the refractive i ndex and impedance depend on the wave propagation direction. This dependen ce – often considered as unwanted – can as I will show bring new inter esting applications to the field of metamaterials. In particular\, it can be used to control the propagation characteristics of optical beams. I wil l also present a model that allows describing the interaction of optical b eams with spatially dispersive metamaterials by making use of a vector ang ular-spectrum representation. Then\, by applying the model\, I will show t hat metamaterial slabs can be designed to have quite demanding functional abilities\, for example\, to act as an apertureless spatial filter or a di ffraction-cancelling beam waveguide. \n\nContact Person: Klas Lindfors LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Satoru Nakatsuji DTSTART;TZID=Europe/Berlin:20150206T140000 DTEND;TZID=Europe/Berlin:20150206T153000 DTSTAMP:20260527T090435Z UID:0000000619@events.thp.uni-koeln.de DESCRIPTION:Satoru Nakatsuji\, ISSP Tokyo\n\nEmergent quantum excitations in spin ice through coupling with electrons\n\nOne of the highlights in th e study of geometrically frustrated magnets is the emergence of nontrivial excitations in spin liquid states\, in particular through the interplay b etween different degrees of freedom\, e.g. between spins and mobile electr ons.\nSuch interesting phenomena have been found in Pr$_2$Ir$_2$O$_7$\, a metallic spin ice with two electronic sectors. One is Pr based spin ice\, where strong quantum effects are expected for ferromagnetic exchange coupl ing and many similarities are found to the quantum spin ice candidate Pr$_ 2$Zr$_2$O$_7$. Another sector is the 5$d$ conduction electrons for which n ovel topological phases have been predicted based on the semimetallic half -filled $J_{¥rm eff} = 1/2$ band due to strong spin-orbit coupling. We wi ll discuss our observations of chiral spin liquid and quantum criticality in Pr$_2$Ir$_2$O$_7$ and topological effects due to semimetallic electroni c structure. \n\n\nContact Person: Simon Trebst LOCATION:Seminarraum Theorie (Neubau) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Theodore L. Einstein DTSTART;TZID=Europe/Berlin:20150206T100000 DTEND;TZID=Europe/Berlin:20150206T110000 DTSTAMP:20260527T090435Z UID:0000000632@events.thp.uni-koeln.de DESCRIPTION:Theodore L. Einstein\, University of Maryland at College Park\ n\nGeneralized Wigner Surmise in the Nanoworld and the Real World: Applica tions to Stepped Surfaces\, Submonolayer Islands\, Metro Stations\, and La ndkreise/Arrondissements\n\n On misoriented ("vicinal") surfaces\, the ter race-width (spacing between adjacent steps) distribution can be related to the spacing distribution of repelling spinless fermions in one dimension\ , and thence to generalizations of the Wigner surmise (GWS) from random-ma trix theory. The GWS expression also emerges as the steady-state solution of a Fokker-Planck description of step evolution. Subsequently we applied this approach to the areas of proximity cells (capture zones) of islands a nd quantum dots on surfaces\; going beyond mean-field is necessary to get the correct relation between the characteristic GWS exponent and the criti cal nucleus size. A fragmentation model offers further insights. I compare analyses of island-size distributions and of scaling of island density vs . flux. I discuss several computer simulations and various experimental ex amples. In particular\, for 6P on mica we need a novel quantitative rate e quation treatment of "hot precursors". Applications to social phenomena in clude the distribution of Metro stations in Paris and the areal distributi on of secondary administrative units (e.g.\, Landkreise and arrondissement s).\n\nContact Person: Joachim Krug LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Eugene Demler DTSTART;TZID=Europe/Berlin:20150211T143000 DTEND;TZID=Europe/Berlin:20150211T160000 DTSTAMP:20260527T090435Z UID:0000000635@events.thp.uni-koeln.de DESCRIPTION:Eugene Demler\, Harvard University\n\nEmergent slow dynamics i n quantum many-body systems\n\nI will discuss several cases where far out of equilibrium dynamics of \nmany-body systems gives rise to emergent quas istationary states\, that \ncan be loosely termed as prethermalized. Examp les include dynamics of \nspin models with either short or long range inte ractions\, quench \ndynamics of Fermi systems starting from a non-interact ing state\, systems \nwith strong disorder\, and systems close to integrab ility\, such as low \ndimensional condensates. This suggests that emergent slow dynamics is a \nuniversal phenomenon of quantum systems. I will revi ew possible \nrealizations of these scenarios in experiments with ultracol d atoms.\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Schüßler-Langheine DTSTART;TZID=Europe/Berlin:20150218T143000 DTEND;TZID=Europe/Berlin:20150218T160000 DTSTAMP:20260527T090435Z UID:0000000618@events.thp.uni-koeln.de DESCRIPTION:Christian Schüßler-Langheine\, Helmholtz Zentrum Berlin\n\nT owards functionality - dynamics studies of complex materials\n\nFunctional ity in materials bases not only on the possibility to affect their propert ies with external stimuli\, but also on the time and length scales such sw itching occurs on. Time-resolved experimental techniques explore switching behavior directly and furthermore provide access to coupling mechanisms b etween different electronic and structural degrees of freedom. In the fiel d of magnetic dynamics\, the laser-induced suppression of helical spin ord er in heavy lanthanide metals reveals a new and very efficient angular-mom entum transfer channel. For the antiferromagnetic semiconductor EuTe we st udied the interplay between magnetic and structural dynamics. For the phot on-pulse-induced Verwey transition in magnetite\, we could further narrow down the time scale on which orbital order decays as well as gain further insight into the character of the low-temperature phase. \n\nContact Perso n: Thomas Koethe LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Daniele Fausti DTSTART;TZID=Europe/Berlin:20150428T130000 DTEND;TZID=Europe/Berlin:20150428T150000 DTSTAMP:20260527T090435Z UID:0000000681@events.thp.uni-koeln.de DESCRIPTION:Daniele Fausti\, University of Trieste and Elettra - Sincrotro ne Trieste\, Italy\n\nWitnessing quasi-particles in a strongly correlated electron system\n\nIn this presentation\, I will introduce the field of ti me domain studies of correlated electron systems focusing on the interacti on between phonons and high-energy excitation of electronic origin in cupr ates. I will review our recent results in archetypal strongly correlated c harge-transfer insulator (La2CuO4) revealing that photo-excitation in corr elated materials pilots the formation of itinerant quasi-particles which a re suddenly dressed (<100 fs) by an ultrafast reaction of the bosonic fiel d. I will introduce our new approach to address correlated electron system s by a full quantum state reconstruction of ultrashort light pulses. I wil l explain Time Resolved Quantum Tomography and show how this provide a new perspective for addressing by time domain studies the quantum state of lo w energy boson in complex materials.\n\nReferences\nNature Comm. 5\, 5112 (2014)\nNew J. Phys. 16 043004 (2014)\n\nContact Person: Paul H. M. van Lo osdrecht LOCATION:Seminar Room\, Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Matthias Batzill DTSTART;TZID=Europe/Berlin:20150506T143000 DTEND;TZID=Europe/Berlin:20150506T160000 DTSTAMP:20260527T090435Z UID:0000000646@events.thp.uni-koeln.de DESCRIPTION:Matthias Batzill\, University of South Florida\, Tampa\, USA\n \nGraphene interfaces: metals\, dielectrics\, and van der Waals materials\ n\n\n\nContact Person: Thomas Michely LOCATION:Seminar Room\, Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Bernard Kippelen DTSTART;TZID=Europe/Berlin:20150513T140000 DTEND;TZID=Europe/Berlin:20150513T153000 DTSTAMP:20260527T090435Z UID:0000000686@events.thp.uni-koeln.de DESCRIPTION:Bernard Kippelen\n\nOrganic electronics: the endless frontier\ n\n\n\nContact Person: Klaus Meerholz LOCATION:Seminar room A\, Chemistry END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Yukitoshi Motome DTSTART;TZID=Europe/Berlin:20150520T143000 DTEND;TZID=Europe/Berlin:20150520T153000 DTSTAMP:20260527T090435Z UID:0000000623@events.thp.uni-koeln.de DESCRIPTION:Yukitoshi Motome\, University of Tokyo\n\nThermodynamics of qu antum spin liquids\n\nThe quantum spin liquid is an exotic quantum state o f matter in magnets\, where conventional symmetry breaking is prevented do wn to the lowest temperature by strong quantum fluctuations. It has attrac ted interest from not only condensed matter physics but also quantum infor mation\, owing to the anticipated topological properties. In order to clar ify the nature of the enigmatic state and explore its realization\, we inv estigate thermodynamic properties of the Kitaev model and its variants\, i n which the exact solutions prove the quantum spin liquids in the ground s tate. We will discuss the surprisingly rich behaviors of quantum spin liqu ids revealed by our numerical simulations\, including (i) thermal fraction alization of quantum spins into Majorana fermions\, (ii) ``liquid-gas" tra nsition by proliferation of loops of excited fluxes\, and (iii) phase diag ram of ``magnetic three states of matter".\n\n\nContact Person: Simon Treb st LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Xenophon Zotos DTSTART;TZID=Europe/Berlin:20150624T143000 DTEND;TZID=Europe/Berlin:20150624T160000 DTSTAMP:20260527T090435Z UID:0000000700@events.thp.uni-koeln.de DESCRIPTION:Xenophon Zotos\, University of Crete\n\nMagnetothermal transpo rt in 1D quantum magnets\n\nI’ll present recent exact results on the fin ite temperature and magnetic field transport in the one dimensional spin-1 /2 Heisenberg model obtained by the Bethe ansatz (BA) method.\nFurthermore \, I’ll discuss the thermodynamics\, thermal transport and ESR of the sp in S=1 easy-plane quasi-one dimensional quantum magnet NiCl2-4SC(NH2)2 (DT N) \nas well as induced magnetisation by light.\n\nContact Person: Thomas Lorenz LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Maxim Dzero DTSTART;TZID=Europe/Berlin:20150701T143000 DTEND;TZID=Europe/Berlin:20150701T160000 DTSTAMP:20260527T090435Z UID:0000000702@events.thp.uni-koeln.de DESCRIPTION:Maxim Dzero\n\nTopological insulators driven by an electron sp in\n\nThe application of ideas developed in topology to the electronic ban d structure led to an intriguing discovery: materials can conduct electric ity at the surface while remaining insulating at the bulk. These materials \, called topological insulators\, will have transformative impact on spin tronics\, low-power transport\, and quantum computing. The search for a tr ue topological insulator took years because even best candidates exhibited significant bulk conductivity. Only recently\, literally in the past few months\, several experimental groups established that samarium hexaboride\ , discovered in 1969 in Bell Labs\, is a first topological insulator in it s bulk form. In my talk\, I review the theory which paved the way for this discovery. I will explain how crystalline symmetry\, electron-electron in teractions\, and orbital degeneracy contribute to protecting the topologic al states in SmB6. In addition\, I will discuss the experimental signature s of metallic surface states as well as the phenomena driven by interactio ns between the chiral electrons. Finally\, I formulate the theoretical pri nciples for discovering new topological insulators with designable propert ies\n\nContact Person: Markus Garst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Catherine Pappas DTSTART;TZID=Europe/Berlin:20150710T130000 DTEND;TZID=Europe/Berlin:20150710T143000 DTSTAMP:20260527T090435Z UID:0000000706@events.thp.uni-koeln.de DESCRIPTION:Catherine Pappas\, TU Delft\n\nMagnetic fluctuations in Multif erroics seen by Neutron Spin Echo spectroscopy\n\n\nNeutron Spin Echo spec troscopy (NSE) is extensively used for the\nstudy of a large variety of sl ow motion phenomena (critical\nslowing down\, relaxation effects\, disorde red dynamics\, soft\nmatter)\, which occur on a mesoscopic time scale betw een\nmicroscopic collision times and macroscopic dynamics. NSE\napplicatio ns in the field of magnetism benefit from the unique\ncombination of high energy resolution with neutron polarization\nanalysis\, which allows a dir ect and unambiguous separation of the\n(often) weak magnetic scattering fr om all other structural\ncontributions. The technique will be introduced and new results\nobtained in collaboration with the Cologne group on the\n multiferroics TbMnO3 and MnWO3 will be discussed.\n\nContact Person: Marku s Braden LOCATION:Seminar Room\, Institute for Theoretical Physics (Main Building) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Alexey Taskin DTSTART;TZID=Europe/Berlin:20150713T160000 DTEND;TZID=Europe/Berlin:20150713T173000 DTSTAMP:20260527T090435Z UID:0000000701@events.thp.uni-koeln.de DESCRIPTION:Alexey Taskin\, Osaka University\n\nNovel Physics in Topologic al Insulator Thin Films\n\nTopological insulators (TIs) realize a new quan tum state of matter where insulating bulk states coexist with metallic sur face states due to a nontrivial Z2 topology of the bulk valence band. I wi ll discuss two prominent examples of novel physics found in TIs for which high-quality thin films grown by molecular beam epitaxy (MBE) are indispen sable: I. A striking manifestation of the topological protection revealed in a systematic evolution of the surface conductance as a function of thic kness in a series of high-quality Bi2Se3 films. II. The observation of unu sual anisotropic magneto-resistance (AMR) and planar Hall effect (PHE) in bulk-insulating (Bi1-xSbx)2Te3 thin films\, for which the concentration of Dirac-like surface carriers\, and consequently the magnitude of AMR and P HE\, can be controlled by electrostatic gating.\n\nContact Person: Achim R osch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Markus Kriener DTSTART;TZID=Europe/Berlin:20150715T143000 DTEND;TZID=Europe/Berlin:20150715T160000 DTSTAMP:20260527T090435Z UID:0000000661@events.thp.uni-koeln.de DESCRIPTION:Markus Kriener\, Center for Emergent Matter Science\, Rieken\, Japan\n\nCompeting Magnetic Phases in the Doped Magnetic Semiconductor Ge Te\n\n\n\nContact Person: Thomas Lorenz LOCATION:Seminar Room\, Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Akira Oiwa DTSTART;TZID=Europe/Berlin:20150814T143000 DTEND;TZID=Europe/Berlin:20150814T160000 DTSTAMP:20260527T090435Z UID:0000000738@events.thp.uni-koeln.de DESCRIPTION:Akira Oiwa\, Osaka University\n\nCoupling between single photo ns to single electron spins in electrically controlled quantum dots\n\nEle ctrical controllability of gate-defined quantum dots (QDs) has brought sig nificant developments in the coherent manipulation of electron spins and t wo-qubit gate operation toward scalable qubits for quantum computations. M oreover the suitability of gate-defined QDs to quantum information technol ogies would be considerably enhanced if spin states in the gate-defined QD s could couple to photon states coherently. Here we show that the photon p olarization can couple to the spin degree of freedom in gate-defined GaAs QDs.\nDouble QDs were fabricated in AlGaAs/GaAs quantum wells[1]. By synch ronizing a pulse laser irradiation with a charge sensing measurement we pe rformed the real-time single photoelectron spin detection in the double QD . First we show that the resonant inter-dot tunneling can offer a robust d etection scheme of the single photoelectrons trapped in the double QDs [2. 3]. In the two-electron regime\, the inter-dot tunneling of the photoelect rons strongly depends on the relative spin orientation (parallel or anti-p arallel) of the two QDs. Therefore by combining the resonant inter-dot tun neling scheme with the Pauli spin effect\, we have realized the nondestruc tive detection of single photoelectron spins. Finally\, we demonstrate the angular momentum conversion from single photons to single electron spins in the double QD from the dependence of the detected spins on the incident photon polarization. We also discuss the future prospects of the photon-s pin quantum interface.\nThis work was done in collaboration with T. Fujita \, K. Morimoto\, G. Allison\, M. Larsson\, H. Kiyama\, S. Teraoka\, S. Haf fouz\, D. G. Austing\, A. Ludwig\, A. D.Wieck and S. Tarucha.\n\n[1] G. Al lison et al.\, Phys. Rev. B 90\, 235310 (2014).\n[2] T. Fujita et al.\, Ph ys. Rev. Lett. 110\, 266803 (2013).\n[3] K. Morimoto et al.\, Phys. Rev. B 90\, 085306 (2014).\n\nContact Person: Yoichi Ando LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Hua Wu DTSTART;TZID=Europe/Berlin:20150819T143000 DTEND;TZID=Europe/Berlin:20150819T160000 DTSTAMP:20260527T090435Z UID:0000000741@events.thp.uni-koeln.de DESCRIPTION:Hua Wu\, Fudan University\n\nSpin-orbit coupling in transition -metal based materials\n\nCurrently 5d transition-metal oxides receive con siderable attention due to their possibly significant spin-orbit coupling (SOC). In this talk\, we will show\, using ab initio calculations\, that t he SOC is indeed important in one-dimensional (1D) and 2D 5d transition-me tal oxides. This is exemplified by addressing the varying magnetic moments in Fe or Co doped Sr2IrO4 [1] and the SOC tuning magnetism in Sr3NiIrO6 [ 2]. However\, the SOC turns insignificant in 3D double perovskites Ca2FeOs O6 and Sr2NiIrO6 due to the band effect. In contrast to the high-temperatu re ferrimagnetism in Ca2FeOsO6 [3]\, an unusual magnetic frustration appea rs in Sr2NiIrO6 [4]. Finally\, we will discuss how to ‘engineer’ a max imum magnetic\nanisotropy in Co\, Ru\, and Os adatoms on MgO (001) surface [5].\n\n[1] X. D. Ou & H. Wu\, PRB 89\, 035138 (2014).\n[2] X. D. Ou & H. Wu\, Sci. Rep. 4\, 4609 (2014).\n[3] H. B. Wang et al.\, PRB 90\, 054406 (2014).\n[4] X. D. Ou et al.\, Sci. Rep. 4\, 7542 (2014).\n[5] X. D. Ou et al.\, submitted (2015).\n\n\nContact Person: Markus Braden LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Marko Kralj DTSTART;TZID=Europe/Berlin:20150826T143000 DTEND;TZID=Europe/Berlin:20150826T160000 DTSTAMP:20260527T090435Z UID:0000000742@events.thp.uni-koeln.de DESCRIPTION:Marko Kralj\, Institute of Physics - Zagreb\n\nComplex structu res based on epitaxial graphene\n\nWhile epitaxial growth secures a source of high-quality graphene for large-scale applications\, it also provides ample possibilities to study and tune the properties of graphene in terms of its structure\, electronic bands or electron correlations. In particula r\, the choice of the substrate and growing conditions can be considered a s a tool to form more complex structures based on epitaxial graphene.\nIn this talk I will first present low energy electron microscopy characteriza tion of graphene on Ir(111) and discuss the "intrinsic" stress-relaxation features\, wrinkles\, which are a result of graphene growth process on man y substrates. It will be shown how the specific substrate interaction lead s to a macroscopic quasi-hexagonal network of wrinkles. Also\, the frustra tion within the network is identified as a governing force for the formati on of complex wrinkle profiles with multiple lobes. Furthermore\, the use of vicinal substrates for the growth of epitaxial graphene will be explore d as a route for the uniaxial engineering of graphene. Based on scanning t unneling microscopy and angle-resolved photoemission spectroscopy experime ntal results as well as van der Waals-density functional theory calculatio ns\, we propose a general mechanism for the observed vicinal substrate res tructuring induced by graphene. Moreover\, by comparing graphene grown on flat and vicinal Ir substrates\, we observe locally variable doping\, the Dirac cone anisotropy\, and a pronounced localization of states at step ed ges. In particular\, the anisotropy is associated to a nanoscale potential modulation induced by the uniaxial pattern\, and the pronounced states to an enhanced chemical binding and charge transfer. We will also show by at omic force microscopy and Raman spectroscopy that upon the transfer of suc h epitaxial graphene to a flat substrate\, the uniaxial strain imposed by the growth process on a vicinal substrate is macroscopically preserved.\n\ nContact Person: Carsten Busse LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Hisao Kobayashi DTSTART;TZID=Europe/Berlin:20150910T143000 DTEND;TZID=Europe/Berlin:20150910T160000 DTSTAMP:20260527T090435Z UID:0000000737@events.thp.uni-koeln.de DESCRIPTION:Hisao Kobayashi\, University of Hyogo\n\nNuclear forward scatt ering of EuFe2As2 under pressure and at low temperature\n\nAfter the disco very of superconductivity in a quasi-two-dimensional LaFeAs(OF) [1]\, the oxygen-free K- doped BaFe2As2 with the well-known quasi-two-dimensional Th Cr2Si2-type (I4/mmm) structure becomes superconducting at 38 K [2]. The pa rent compound\, AFe2As2 (A = Ca\, Eu\, Sr\, and Ba)\, undergoes a commensu rate spin density wave (SDW) antiferromagnetic transition. This SDW transi tion in AFe2As2 is suppressed by applied pressure\, giving rise to superco nductivity at low temperature. Since pressure tuning of a stoichiometric c ompound is a powerful technique for understanding phase transitions\, AFe2 As2 is promising candidate for studying the mechanism of superconductivity in these iron arsenide compounds.\nThe 57Fe and 151Eu nuclear forward sca ttering (NFS) experiments under high pressure at low temperatures were car ried out using the EuFe2As2 single-crystal sample on the NE1 beamline at t he accumulation ring of the High Energy Accelerator Research Organization and on the BL09XU beamline at SPring-8 to investigate the correlation betw een magnetism and superconductivity in the pressure-induced EuFe2As2 super conductor.\nWe find a microscopic coexistence of magnetism at the Fe and E u sublattices and bulk superconductivity under pressure and at low tempera ture. The magnetic structure of the Fe sublattice changes to a modified an tiferromagnetic structure in the superconducting state from the commensura te stripe-type antiferromagnetic one in the normal conducting state below 3 GPa. This modified antiferromagnetic structure in the superconducting st ate has never been observed in the magnetic ordered states in AFe2As2 unde r pressure and in substituted AFe2As2. The modified antiferromagnetic stat e with superconductivity in EuFe2As2 under pressure most likely is caused by the change of the electronic state of the Fe atom due to the effective As-As hybridization induced by pressure in the tetragonal symmetry of the crystal structure [3]. Furthermore\, the order parameter of the modified a ntiferromagnetic state does not compete with that of superconductivity in the pressure-induced EuFe2As2 superconductor.\nReferences\n[1] Y. Kamihara \, et al.\, J. Am. Chem. Soc. 130\, 3296 (2008). [2] M. Rotter\, et al.\, Phys. Rev. Lett. 101\, 107006 (2008). [3] H. Kobayashi\, et al.\, J. Phys. : Condens. Matter 25\, 022201 (2013).\n\nContact Person: Mohsen Abd-Elmegu id LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Ian Affleck DTSTART;TZID=Europe/Berlin:20150923T143000 DTEND;TZID=Europe/Berlin:20150923T160000 DTSTAMP:20260527T090435Z UID:0000000753@events.thp.uni-koeln.de DESCRIPTION:Ian Affleck\, University of Vancouver\n\nOrbital Kondo Effect in Fractional Quantum Hall Systems\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dirk Honecker DTSTART;TZID=Europe/Berlin:20150930T143000 DTEND;TZID=Europe/Berlin:20150930T160000 DTSTAMP:20260527T090435Z UID:0000000746@events.thp.uni-koeln.de DESCRIPTION:Dirk Honecker\, Institut Laue-Langevin\, Grenoble \n\nMagnetic small-angle neutron scattering of bulk ferromagnets\n\n\n\nContact Person : Sabrina Disch LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Katharina J. Franke DTSTART;TZID=Europe/Berlin:20151021T143000 DTEND;TZID=Europe/Berlin:20151021T160000 DTSTAMP:20260527T090435Z UID:0000000682@events.thp.uni-koeln.de DESCRIPTION:Katharina J. Franke\, Freie Universität Berlin\n\nMagnetic p roperties of single molecules on surfaces probed by scanning tunneling spe ctroscopy\n\nThe magnetic properties of single atoms are significantly aff ected by details in the atomic- scale surrounding. One strategy to control the spin state and magnetic anisotropy is to embed the atoms into specifi cally designed organic ligands. Moreover\, the surface plays a pivotal rol e in the magnetic properties when it interacts with the magnetic core. Her e\, we utilize scanning tunneling microscopy and spectroscopy to character ize the magnetic anisotropy and lifetimes of excited states of single para magnetic molecules on a surface and point out possibilities to tune these. \n\nContact Person: Dirk Hertel LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Giulio Monaco DTSTART;TZID=Europe/Berlin:20151116T150000 DTEND;TZID=Europe/Berlin:20151116T160000 DTSTAMP:20260527T090435Z UID:0000000792@events.thp.uni-koeln.de DESCRIPTION:Giulio Monaco\, University of Trento\n\nInelastic X-ray scatte ring experiments to probe electronic excitations\n\nInelastic X-ray scatte ring at third generation synchrotron sources is a technique gaining an inc reasing interest from a growing community of users. Referring to the capab ilities of beamline ID20 at the ESRF\, I will recall the main fields of ac tivity for IXS to probe electronic excitations in condensed matter\, focus ing in particular on resonant inelastic X-ray scattering experiments at th e Ir L3 edge.\n\nContact Person: Paul van Loosdrecht LOCATION:Conference Room II\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Frank Meyer zu Heringdorf DTSTART;TZID=Europe/Berlin:20151209T143000 DTEND;TZID=Europe/Berlin:20151209T160000 DTSTAMP:20260527T090435Z UID:0000000791@events.thp.uni-koeln.de DESCRIPTION:Frank Meyer zu Heringdorf\, University of Duisburg-Essen\n\nPl asmoemission: Emission of Electrons in a strong Plasmonic Field\n\n\n\nCo ntact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Vincent Cros DTSTART;TZID=Europe/Berlin:20151221T160000 DTEND;TZID=Europe/Berlin:20151221T173000 DTSTAMP:20260527T090435Z UID:0000000797@events.thp.uni-koeln.de DESCRIPTION:Vincent Cros\, Universite Paris-Sud\n\nSub-100 nm skyrmions at room temperature: From magnetic thin films to asymmetric magnetic multila yers\n\n\n\nContact Person: Jan Mueller LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Fabian Heidrich-Meisner DTSTART;TZID=Europe/Berlin:20160120T143000 DTEND;TZID=Europe/Berlin:20160120T160000 DTSTAMP:20260527T090435Z UID:0000000804@events.thp.uni-koeln.de DESCRIPTION:Fabian Heidrich-Meisner\, LMU Munich\n\nSpin and heat transpor t in low-dimensional quantum magnets\n\n\n\nContact Person: Matteo Montagn ese LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Regina Dittmann DTSTART;TZID=Europe/Berlin:20160413T143000 DTEND;TZID=Europe/Berlin:20160413T160000 DTSTAMP:20260527T090435Z UID:0000000848@events.thp.uni-koeln.de DESCRIPTION:Regina Dittmann\, Forschungszentrum Juelich\n\nUncovering nano scale changes in the electronic structure during the operation of complex oxide memristive devices\n\nOxide-based memristive devices\, which exhibit two or more resistive states under electrical biasing\, are promising can didates for future non-volatile memories as well as for active elements fo r neuromorphic computing. It has become widely accepted that memristive sw itching in oxides is in most cases connected with a voltage-driven oxygen vacancy movement and a resulting metal-to-insulator transition. However\, the current knowledge of the microscopic details is very limited so far. O ne of the obstacles for its further elucidation has been that the net chan ges of the atomic and electronic structure during memristive switching are very small and occur primarily at the electrode interface or within nanos cale filaments. \nBy employing different approaches of X-ray based spectro microscopy\, we could prove the formation of an oxygen vacancy enriched fi lament in epitaxial SrTiO3 thin film devices\, which occurs preferentially at preformed positions such as extended defects. For high current operati on\, electric biasing goes along with the formation of SrO at the electrod e interface which has a significant impact on the stabilization of the res istance states of the devices. \nIn operando studies of SrTiO3 devices wit h photoelectron-transparent graphene electrodes enabled us to detect rever sible changes of the O K-edge spectra within spatially confined regions of the devices. Based on these results\, we obtain for the first time a quan titative estimate of the amount of oxygen vacancies shifted during the swi tching process.\n\n\nContact Person: not specified LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Steven Mathey DTSTART;TZID=Europe/Berlin:20160504T143000 DTEND;TZID=Europe/Berlin:20160504T153000 DTSTAMP:20260527T090435Z UID:0000000875@events.thp.uni-koeln.de DESCRIPTION:Steven Mathey\, University of Grenoble\n\nNon-Equilibrium inte rface dynamics with correlated noise: Emergent symmetries and non-universa l observables\n\nThe Kardar-Parisi-Zhang (KPZ) equation provides one of th e simplest non trivial examples of a Non-Equilibrium Steady State. Its uni versal features capture a very wide range of physical phenomena ranging fr om varied types of interfaces to turbulent hydrodynamic flows or thermodyn amics of polymers in noisy environments. Enormous progress has been made i n the last 10 years thanks to an exact derivation of the statistics of the KPZ dynamics in the case of one-dimensional systems driven by a stochasti c white noise. The cases of higher dimensions and/or\ncorrelated noise rem ain however unsolved. \n\nIn this presentation I discuss the physics of a one-dimensional interface that is subjected to a noise with smooth spatio- temporal correlations. This problem was previously studied numerically as well as with the Replica Trick in a Gaussian variational approach.It was f ound that the small scale features depend on the details of the microscopi c noise while (up to the overall amplitude factors) the exact solution wit h white noise governs the large scales. In the present work\, Functional R enormalisation Group (FRG) methods are employed in order to resolve the no n-perturbative features of KPZ dynamics. The FRG makes it possible to foll ow the renormalisation group flow from its initial conditions all the way down to its fixed point\, that is from microscopic dynamics to the large d istance properties. I show that the exact solution emerges on large scales independently of the details of the\nnoise correlations. Moreover the sma ll scale features (and their dependence on the particular choice of the no ise correlations) are resolved and compared to direct numerical simulation s.\n\nContact Person: Sebastian Diehl LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Hendrik Bluhm DTSTART;TZID=Europe/Berlin:20160511T143000 DTEND;TZID=Europe/Berlin:20160511T160000 DTSTAMP:20260527T090435Z UID:0000000870@events.thp.uni-koeln.de DESCRIPTION:Hendrik Bluhm\, RWTH Aachen\n\nSpin qubits in GaAs quantum dot s - an experimental perspective on the central spin problem and quantum co ntrol\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Claus Schneider DTSTART;TZID=Europe/Berlin:20160518T143000 DTEND;TZID=Europe/Berlin:20160518T160000 DTSTAMP:20260527T090435Z UID:0000000873@events.thp.uni-koeln.de DESCRIPTION:Claus Schneider\, FZ Juelich\n\nJuSPARC - Probing the solid st ate at ultrafast timescales\n\nProcesses involving electrons and spins oft en take place on sub-picosecond timescales. This is particularly true for electronic phase transitions\, ultrafast demagnetization\, or local redox processes during resistive switching. The rapid development in femtosecond laser sources enables new experimental avenues which open the access to t he electronic\, spin\, and lattice response on such ultrashort timescales. With JuSPARC we plan to establish a unique experimental environment to ex plore ultrafast processes in condensed matter by means of spectroscopy\, m icroscopy and scattering techniques.\n\nContact Person: Paul van Loosdrech t LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Bernard Kippelen DTSTART;TZID=Europe/Berlin:20160525T143000 DTEND;TZID=Europe/Berlin:20160525T160000 DTSTAMP:20260527T090435Z UID:0000000869@events.thp.uni-koeln.de DESCRIPTION:Bernard Kippelen\, Georgia Institute of Technology\n\nOrganic Electronics: Finding Simplicity in Complexity\n\nConjugated organic molecu les and polymers enable the demonstration of flexible semiconductor device s that can be processed at low temperature onto different substrates with variable form factors. Over the past decades\, device performance has impr oved greatly as a large number of new compounds were synthesized and teste d in various device geometries. While molecular-level models have been suc cessful in providing a rational design of molecules and polymers for highe r performance\, models to predict the morphology of thin films and consequ ently macroscopic physical properties\, such as charge mobility\, remain e lusive. The lack of such models has resulted in a trial and error approach and limits our ability to predict ultimate performance. Furthermore\, org anic solids exhibit photophysical properties that are unique and different from those of conventional inorganic semiconductors. The question then ar ises whether semiconductor equations developed for inorganic semiconductor devices can be applied to describe the physical properties of organic ele ctronic devices. In this talk\, we will highlight some fundamental differe nces in the physical properties between organic and inorganic semiconducto rs\, but show that general models such as the Shockley diode equation can be applied to organic photodiodes and solar cells. In particular\, we will emphasize the importance to understand and mitigate parasitic effects suc h as shunt resistance effects in these devices as they often overshadow th e intrinsic physical properties and can lead to different interpretations of results.\n\nContact Person: Klaus Meerholz LOCATION:Seminar Room\, Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Ruslan Temirov DTSTART;TZID=Europe/Berlin:20160601T143000 DTEND;TZID=Europe/Berlin:20160601T160000 DTSTAMP:20260527T090435Z UID:0000000842@events.thp.uni-koeln.de DESCRIPTION:Ruslan Temirov\, FZ Juelich\n\nManipulation and control of mol ecular degrees of freedom with a scanning probe microscope\n\n\n\nContact Person: Thomas Michely LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Grace Lu DTSTART;TZID=Europe/Berlin:20160614T140000 DTEND;TZID=Europe/Berlin:20160614T153000 DTSTAMP:20260527T090435Z UID:0000000896@events.thp.uni-koeln.de DESCRIPTION:Grace Lu\, USC Los Angeles\n\nSemiconductor and Magnetic Nanow ires\n\n\n\nContact Person: Achim Rosch LOCATION:HS II\, Institute of Physics END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Alexander Ako Khajetoorians DTSTART;TZID=Europe/Berlin:20160615T143000 DTEND;TZID=Europe/Berlin:20160615T160000 DTSTAMP:20260527T090435Z UID:0000000843@events.thp.uni-koeln.de DESCRIPTION:Alexander Ako Khajetoorians\, Radboud University\n\nSpin sensi ng and magnetic design at the single atom level\n\n\n\nContact Person: Tho mas Michely LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Mukul Laad DTSTART;TZID=Europe/Berlin:20160628T160000 DTEND;TZID=Europe/Berlin:20160628T170000 DTSTAMP:20260527T090435Z UID:0000000878@events.thp.uni-koeln.de DESCRIPTION:Mukul Laad\, University of Chennai\n\nA First-Principles Corre lated Approach to the Normal State of Layered Strontium Ruthenate\n\n Unco nventional Superconductivity (USC) in layered Sr$_{2}$RuO$_{4}$\nis of lon g-standing interest because it is long thought to be a\nsuperconducting an alogue of $^{3}He$. However\, resurgence of recent\ndata points toward a much more involved pairing symmetry\, where the\ninterplay between multi-b and character\, sizable multi-band\nelectronic correlations and strong spi n-orbit coupling conspires to\nselect an apparently rather unusual\, hithe rto unknown\, USC pair\nsymmetry. This mandates detailed revisiting of th e normal state\nand\, in particular\, of the $T$-dependent incoherence-coh erence\ncrossover. Here\, using a modern first-principles correlated view \,\nwe study this issue in the real structure of Sr$_{2}$RuO$_{4}$ in\ndet ail and present a unified and quantitative description of a range\nof unus ual physical responses in the normal state across the\ncrossover. Armed w ith these strengths\, we propose that a new and\nimportant element\, that of dominant (quasi-one-dimensional $xz\,yz$)\ninterband charge fluctuation s in a ``Hund'' metal\, may be a primary\npair glue for USC in this system . We will emphasize internal\nconsistency of our proposed scenario vis-a- vis a wide range of\nconstraints imposed by extant data.\n\nContact Person : Simon Trebst LOCATION:Seminar Room Kernphysik END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Qimiao Si DTSTART;TZID=Europe/Berlin:20160629T143000 DTEND;TZID=Europe/Berlin:20160629T160000 DTSTAMP:20260527T090435Z UID:0000000891@events.thp.uni-koeln.de DESCRIPTION:Qimiao Si\, Rice University\n\nFrustrated Magnetism and Superc onductivity in Iron Pnictides and Chalcogenides\n\n\n\nContact Person: not specified LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Michael Ziese DTSTART;TZID=Europe/Berlin:20160713T110000 DTEND;TZID=Europe/Berlin:20160713T123000 DTSTAMP:20260527T090435Z UID:0000000903@events.thp.uni-koeln.de DESCRIPTION:Michael Ziese\, Leipzig University\n\nMagnetic and Magnetotran sport Properties of Superlattices with Ultrathin SrRuO3 Layers\n\nHeterost ructures with ultrathin layers are an exciting playground for materials sc ience\, since quantum confinement and interfacial properties often lead to new functionalities. In this talk a survey is given of the magnetic and m agnetotransport properties of SrRuO3/manganite superlattices and trilayers . The itinerant ferromagnet SrRuO3 has a comparatively high conductivity a nd large magnetocrystalline anisotropy and can be grown in excellent quali ty in these all-perovskite heterostructures. The properties of the superla ttices are rather complex showing a transition from orthorhombic to tetrag onal crystalline symmetry of the SrRuO3 layers coupled with large changes in the magnetocrystalline and magnetoresistance anisotropy. Embedding of L a0.7Ba0.3MnO3 within SrRuO3 layers leads to the stabilization of ferromagn etism above 150 K in single unit cell thick manganite layers. This appears to be related to an interfacial anomalous Hall effect observed in the sup erlattices.\n\nContact Person: Ionela Verjoiu LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Mohammad Faghfoor Maghrebi DTSTART;TZID=Europe/Berlin:20160721T100000 DTEND;TZID=Europe/Berlin:20160721T110000 DTSTAMP:20260527T090435Z UID:0000000926@events.thp.uni-koeln.de DESCRIPTION:Mohammad Faghfoor Maghrebi\, University of Maryland\n\nSteady states and dynamics in many-body driven-dissipative systems\n\nMany-body s ystems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipatio nless counterparts. The advent of numerous experimental platforms that sim ulate such dynamics poses an immediate challenge to systematically underst and and classify these models. In particular\, nontrivial many-body states emerge as steady states under non-equilibrium dynamics. In this talk\, I use a systematic approach to study nonequilibrium phases and phase transit ions and the dynamics in such models. I show that an effective thermal beh avior generically emerges as a result of dissipation. Finally I use this e quivalence to make quantitative predictions about the properties of the st eady-state its dynamical properties.\n\nContact Person: Sebastian Diehl LOCATION:Seminarroom 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Wulf Wulfhekel DTSTART;TZID=Europe/Berlin:20160921T143000 DTEND;TZID=Europe/Berlin:20160921T160000 DTSTAMP:20260527T090435Z UID:0000000909@events.thp.uni-koeln.de DESCRIPTION:Wulf Wulfhekel\, KIT\n\nMolecular systems for spintronics and mechatronics\n\n\n\nContact Person: Thomas Michely LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Masatoshi Sato DTSTART;TZID=Europe/Berlin:20160922T140000 DTEND;TZID=Europe/Berlin:20160922T153000 DTSTAMP:20260527T090435Z UID:0000000939@events.thp.uni-koeln.de DESCRIPTION:Masatoshi Sato\, Kyoto University\n\nNonsymmorphic Symmetry an d New Topological Phases\n\nNonsymmorphic symmetry is crystal symmetry rea lized as combination of a point group operation and a non-primitive lattic e translation. Many crystals have such nonsymmorphic crystal symmetry\, bu t it effects on topological phases just begin to be explored very recently . It has been discovered that nonsymmorphic symmetry provides intrinsicall y new topological phases in insulators and superconductors. For example\, the new topological phases may be characterized by new Z2 and Z4 topologic al indices\, hosting exotic Mobius twisted surface states. In addition\, n onsymmorphic symmetry also provides new gapless structure in nodal superco nductors. In this talk\, I will explain our recent results on nonsymmorphi c topological phases.\n\nContact Person: Yoichi Ando LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Leonhard Grill DTSTART;TZID=Europe/Berlin:20161005T143000 DTEND;TZID=Europe/Berlin:20161005T160000 DTSTAMP:20260527T090435Z UID:0000000877@events.thp.uni-koeln.de DESCRIPTION:Leonhard Grill\, University of Graz\n\nAssembly and characteri zation of single functional molecules on surfaces\n\nFunctional molecules on surfaces and their assembly into pre-defined architectures are key chal lenges in nanotechnology and of interest in various fields from molecular electronics over novel materials to molecular machines. Various examples o f functional molecules\, studied by scanning tunneling microscopy (STM) un der ultrahigh vacuum conditions\, will be discussed. Specifically designed molecular building blocks are connected to two-dimensional networks or on e-dimensional chains\, which can act as molecular wires. On the other hand \, chemical processes within individual molecular can be controlled via th eir environment. This was observed for molecular switches\, where the atom ic-scale surroundings cause drastic changes in their switching probability . It could be shown that the rate of an intramolecular hydrogen transfer r eaction can be tuned up and down by single atoms in the vicinity of the mo lecule. Single atoms were also found to modify the appearance of adsorbed molecules in STM images during their diffusion underneath the molecules. A combination of the two approaches will be discussed\, potentially leading to heterogeneous molecular nanostructures that contain functional molecul es.\n\nContact Person: Alexander Grueneis LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Hiroki Isobe DTSTART;TZID=Europe/Berlin:20161013T140000 DTEND;TZID=Europe/Berlin:20161013T153000 DTSTAMP:20260527T090435Z UID:0000000969@events.thp.uni-koeln.de DESCRIPTION:Hiroki Isobe\, MIT\n\nInterlayer pairing symmetry of composite fermions in quantum Hall bilayers\n\nSince the discovery of quantum Hall effect\, two-dimensional electron system under magnetic field has provided lots of intriguing physics topics both experimentally and theoretically\, including integer/fractional quantized Hall conductance\, anyon statistic s\, and non-Abelian particles. Electron-electron interactions play crucia l roles in such quantum Hall problems. Even richer phenomena take place f or two parallel two-dimensional sheets. Bilayer systems\, or more general ly multicomponent systems\, have additional degrees of freedom\, and they allow interlayer paired states at even-denominator filling fraction in eac h layer\, which exhibits the Fermi sea of composite fermions without inter actions. I will discuss the interlayer paired state in the presence of th e Coulomb interaction and its pairing symmetry\, and will make a comment o n a possible topological order of the ground state.\n\nContact Person: Yoi chi Ando LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Michael Kiessling DTSTART;TZID=Europe/Berlin:20161026T143000 DTEND;TZID=Europe/Berlin:20161026T160000 DTSTAMP:20260527T090435Z UID:0000000942@events.thp.uni-koeln.de DESCRIPTION:Michael Kiessling\, Rutgers University\n\nOn the quantum mecha nics of a single photon\n\nThe quantum mechanical wave equation for a sing le photon is conspicuously missing from textbooks on quantum mechanics. Op inions range from the claim that this notion is meaningless to suggestions that Maxwell's\nelectromagnetic field equations supply it in disguise. Af ter reviewing the arguments pro and con\, we will propose a Lorentz covar iant wave equation for a photon and demonstrate that it possesses the desi rable features. This is joint work with A. Shadi Tahvildar-Zadeh.\n\nConta ct Person: Markus Kunze LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Sebastian Loth DTSTART;TZID=Europe/Berlin:20161102T143000 DTEND;TZID=Europe/Berlin:20161102T160000 DTSTAMP:20260527T090435Z UID:0000000912@events.thp.uni-koeln.de DESCRIPTION:Sebastian Loth\, MPI\n\nHarnessing quantum effects in atom-siz ed antiferromagnets\n\nAntiferromagnets are often used only for their resi lience to external magnetic fields and appear ill-suited for use as active elements in spintronic devices. But when shrunk to nanometer dimensions a ntiferromagnets gain in functionality. We use low-temperature scanning tun neling microscopy to create small antiferromagnets of our own design atom by atom. At this extreme scale of individual atoms we can begin to harness quantum mechanical effects. \nIn this way we can build antiferromagnetic nanostructures that show two stable magnetic states with no net magnetic m oment or structures that have a unique ground state but feature rich magne tic dynamics of their excited states. I will introduce how inter-atomic ex change bias gives control over the spin ground state and excitation dynami cs of antiferromagnets and demonstrate how coupling to the dissipative env ironment can be used to stabilize spins.\n\n\nContact Person: Thomas Miche ly LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Steve Zelditch DTSTART;TZID=Europe/Berlin:20161123T160000 DTEND;TZID=Europe/Berlin:20161123T173000 DTSTAMP:20260527T090435Z UID:0000000983@events.thp.uni-koeln.de DESCRIPTION:Steve Zelditch\, Northwestern University\n\nHow to fill a doma in with quantum states in quantum Hall problems\n\nLet D be a domain in so me surface M. In fact\, M could have any dimension. We would like to const ruct global quantum states on M which are localized in D and completely fi ll up D without much spillover outside D. We answer the question by making the quantum states eigenstates of a certain Hamiltonian defined so that D is the energy set H < E. The projection onto the corresponding eigenspace s defines a partial Bergman kernel and when normalized properly\, it tends to 1 on D and zero outside D as Planck's constant tends to zero. There is a universal transition from 0 to 1.\n\nContact Person: George Marinescu LOCATION:Lecture Hall VIII\, Main Building END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Mikhail Katsnelson DTSTART;TZID=Europe/Berlin:20161208T160000 DTEND;TZID=Europe/Berlin:20161208T173000 DTSTAMP:20260527T090435Z UID:0000000995@events.thp.uni-koeln.de DESCRIPTION:Mikhail Katsnelson\, University of Nijmegen\n\nGauge fields an d strain engineering in graphene\n\n\nIt is demonstrated now both experime ntally and theoretically that graphene is usually not flat but covered by ripples resulting from both intrinsic flexural instability of two-dimensio nal membranes and roughness of substrate. Thus charge carriers are not jus t Dirac fermions but Dirac fermions moving in a curved space. The effect o f the corrugations on the electron spectrum can be described in terms of g auge (pseudo-magnetic) fields which result\, in particular\, in formation of pseudo-Landau levels predicted theoretically and found experimentally . These gauge fields can be used for "strain engineering"\, including tunab le gap opening\, quantum pumping [and creation of valley-polarized current . Ripples can induce puddles\, that is\, charge inhomogeneities. The scatt ering by the ripples is also one of the limiting factors restricting the c harge carrier mobility in graphene.\n\n\nContact Person: George Marinescu LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Bjoern Trauzettel DTSTART;TZID=Europe/Berlin:20170201T143000 DTEND;TZID=Europe/Berlin:20170201T160000 DTSTAMP:20260527T090435Z UID:0000000994@events.thp.uni-koeln.de DESCRIPTION:Bjoern Trauzettel\, University of Wuerzburg\n\nChiral anomaly in real space from stable fractional charges at the edge of a quantum spin Hall insulator\n\nThe chiral anomaly is based on a non-conserved chiral c harge and can happen in Dirac fermion systems under the influence of exter nal electromagnetic fields. In this case\, the spectral flow leads to a t ransfer of right- to left-moving excitations or vice versa. The correspond ing transfer of chiral particles happens in momentum space. We here descri be an intriguing way to introduce the chiral anomaly into real space. Our system consists of two quantum dots that are formed at the helical edges o f a quantum spin Hall insulator by means of magnetic barriers. Such a setu p gives rise to fractional charges which we show to be sharp quantum numbe rs for large barrier strength.\nInterestingly\, it is possible to map the system onto a quantum spin Hall ring in the presence of a flux pierced thr ough the ring where the relative angle between the magnetization direction s of the barriers takes the role of the flux. The chiral anomaly in this s ystem is then directly related to the excess occupation of particles in th e two quantum dots. This analogy allows us to predict an observable conseq uence of the chiral anomaly in real space.\n\nContact Person: Alex Altland LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Michael Knap DTSTART;TZID=Europe/Berlin:20170301T143000 DTEND;TZID=Europe/Berlin:20170301T160000 DTSTAMP:20260527T090435Z UID:0000000987@events.thp.uni-koeln.de DESCRIPTION:Michael Knap\, TU Munich\n\nNonequilibrium dynamics in diffusi ve many-body systems: from scrambling to heating\n\nIn this talk\, we will discuss our recent results on scrambling of quantum information and therm alization in the one-dimensional Bose-Hubbard model. Numerically exact res ults are presented for the out-of-time (OTO) as well as time ordered corre lation functions using matrix product operator techniques. I will also giv e a short account on how to measure such OTO correlators in quantum gas mi croscopes. If time permits\, we will also discuss pre-thermalization and h eating dynamics in the periodically driven Bose-Hubbard model and a relate d O(N) field theory. Relevant references include:\n[1] Scrambling and ther malization in a diffusive quantum many-body system. A. Bohrdt\, et al. [ar Xiv:1612.02434]\n[2] Floquet prethermalization and regimes of heating in a periodically driven\, interacting quantum system. S. Weidinger\, et al. [ arXiv:1609.09089]\n[3] Prethermal Floquet steady-states and instabilities in the periodically-driven\, weakly-interacting Bose-Hubbard model. M. Buk ov et al. Phys. Rev. Lett. 115\, 205301 (2015) [arXiv:1507.01946]\n\nConta ct Person: Jamir Marino LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Peter Prelovsek DTSTART;TZID=Europe/Berlin:20170403T140000 DTEND;TZID=Europe/Berlin:20170403T153000 DTSTAMP:20260527T090435Z UID:0000001048@events.thp.uni-koeln.de DESCRIPTION:Peter Prelovsek\n\nMany-body localization - search for an idea l nonequilibrium system\n\nMany-body localization (MBL) is the quantum phe nomenon involving the interplay of disorder and particle interaction\, ch aracterized by the nonergodic behaviour of physical observables. It is int ensively investigated theoretically within disordered many-body models and experimentally in optical lattices of cold atoms. Within a one-dimensiona l random-field spin system dynamical density correlations can be used as an indicator for the MBL phase and are closely related to the dynamical sp in conductivity and d.c. transport. \nAn analytical approach indicates th at one dimension might still be singular with the subdiffusion in the ergo dic phase. On the other hand\, an analogous simulation of the Hubbard chai n shows that a disordered potential does not induce full MBL\, but only c harge localisation.\n\n\nContact Person: Zala Lenarcic LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Sergej Moroz DTSTART;TZID=Europe/Berlin:20170405T143000 DTEND;TZID=Europe/Berlin:20170405T160000 DTSTAMP:20260527T090435Z UID:0000001052@events.thp.uni-koeln.de DESCRIPTION:Sergej Moroz\n\nTopological order\, symmetry\, and Hall respon se of two-dimensional spin-singlet superconductors\n\n\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Marco Schiro DTSTART;TZID=Europe/Berlin:20170419T143000 DTEND;TZID=Europe/Berlin:20170419T153000 DTSTAMP:20260527T090435Z UID:0000001013@events.thp.uni-koeln.de DESCRIPTION:Marco Schiro\n\nQuantum Many Body Physics with Strongly Intera cting Matter and Light \n\nDevelopments in quantum optics and quantum engi neering have brought forth the possibility of studying emergent collective phenomena in hybrid quantum light-matter systems. \nThese platforms\, whi ch are intrinsically driven and dissipative\, allow to probe fundamental m any body physics in uncharted territories. \nIn this talk I will discuss t he steady state properties of paradigmatic lattice models of photons coupl ed to qubits\, highlighting those aspects of the physics which are genuine nonequilibrium features \nand cannot be understood even qualitatively fro m an effective equilibrium. I will then discuss the role of non-Markovian bath correlations on a prototypical light-matter phase transition\, \nthe Dicke superradiance of N qubits coupled to a cavity\, and show that ohmic/ subohmic environemnts can induce a dissipative phase transition surving ev en at finite N\, \nsmoothly connected to the well studied Caldeira-Leggett /spin-boson one. Finally\, I will present our ongoing effort to develop a new approach to driven-dissipative lattice models\, \nbased on non-equilib rium dynamical mean field theory.\n\nContact Person: Jamir Marino LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Roger Melko DTSTART;TZID=Europe/Berlin:20170426T143000 DTEND;TZID=Europe/Berlin:20170426T160000 DTSTAMP:20260527T090435Z UID:0000001029@events.thp.uni-koeln.de DESCRIPTION:Roger Melko\, University of Waterloo\, Perimeter Institute\n\n Quantum machine learning\n\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Kamran Behnia DTSTART;TZID=Europe/Berlin:20170516T143000 DTEND;TZID=Europe/Berlin:20170516T160000 DTSTAMP:20260527T090435Z UID:0000001081@events.thp.uni-koeln.de DESCRIPTION:Kamran Behnia\, ESPCI ParisTech\n\nBerry Curvature and entropy flow in Mn3Sn\, a non-collinear magnet metal with Weyl nodes\n\n\n\nConta ct Person: Joachim Hemberger LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Karen Michaeli DTSTART;TZID=Europe/Berlin:20170621T143000 DTEND;TZID=Europe/Berlin:20170621T154500 DTSTAMP:20260527T090435Z UID:0000001023@events.thp.uni-koeln.de DESCRIPTION:Karen Michaeli\, Weizmann Institute of Science\n\nSuperconduct ivity in the Presence of Spin-Orbit Coupling — Old Dog\, New Tricks\n\nT he coupling between the spin of an electron and its momentum is recognized to generate a variety of new phases in condensed matter systems. For exam ple\, it has been recently demonstrated that spin-orbit coupling can chang e the nature of a trivial insulator to endow it with topological propertie s. Or\, in symmetry broken states\, spin-orbit coupling permits exotic low energy excitations such as skyrmions in helimagnets. The interplay betwee n superconductivity and spin-orbit effects gives rise to additional surpri sing features\, which I will discuss in my talk. For instance\, it stabili zes a condensate of Cooper pairs with finite momentum (a variant of the Fu lde-Ferrel-Larkin-Ovchinikov state) up to high magnetic fields. Even more surprisingly\, in the presence of spin-orbit coupling the transition tempe rature into the superconducting state may increase under application of a Zeeman magnetic field. Furthermore\, such superconductors can exhibit pe rsistent currents without magnetic fields in doubly connected geometries.\ n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Jan Carl Budich DTSTART;TZID=Europe/Berlin:20170705T143000 DTEND;TZID=Europe/Berlin:20170705T160000 DTSTAMP:20260527T090435Z UID:0000001108@events.thp.uni-koeln.de DESCRIPTION:Jan Carl Budich\, University of Innsbruck\n\nTopological Quant um Matter far from Equilibrium\n\nTopological states of quantum matter suc h as topological insulators and superconductors have been an active field of research in physics for many years. The recent experimental progress on their realization with ultracold atomic gases raises natural questions ab out the notion of topological quantum matter far from thermal equilibrium. In this talk\, we present our theoretical findings in this context.\n\nWe first discuss the non-equilibrium Hall response of a system initialized i n a topologically trivial state before its Hamiltonian is ramped into a Ch ern insulator phase\, comparing the coherent dynamics with effects of deph asing. In the second part of the talk\, we discuss non-equilibrium proper ties of driven systems. In particular\, we show how a perfect spin momentu m locking\, so far only known from edge states of two-dimensional topologi cal insulators can emerge in the stroboscopic dynamics of one-dimensional Floquet lattice systems. Finally\, we discuss dynamically defined topologi cal quantum numbers that have no non-equilibrium counterpart\, and report on their very recent experimental observation.\n\nContact Person: Sebastia n Diehl LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Karsten Flensberg DTSTART;TZID=Europe/Berlin:20170712T143000 DTEND;TZID=Europe/Berlin:20170712T160000 DTSTAMP:20260527T090435Z UID:0000001046@events.thp.uni-koeln.de DESCRIPTION:Karsten Flensberg\, Niels-Bohr-Institute\, Copenhagen\n\nMajor ana wires: towards non-local quantum states\n\n\n\nContact Person: Altland / Trebst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Andrei Marshakov DTSTART;TZID=Europe/Berlin:20170926T143000 DTEND;TZID=Europe/Berlin:20170926T160000 DTSTAMP:20260527T090435Z UID:0000001128@events.thp.uni-koeln.de DESCRIPTION:Andrei Marshakov\, Skoltech\, Moscow\n\nModern applications of 2d CFT\n\n\n\nContact Person: Semyon Klevtsov LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Sabrina Disch DTSTART;TZID=Europe/Berlin:20171115T143000 DTEND;TZID=Europe/Berlin:20171115T153000 DTSTAMP:20260527T090435Z UID:0000001104@events.thp.uni-koeln.de DESCRIPTION:Sabrina Disch\, Department Chemie\, University of Cologne\n\nM agnetic structure on the Nanoscale: Intraparticle Magnetization and Interp article Interactions\n\nMagnetic nanoparticles reveal unique magnetic prop erties and relaxation phenomena which make them relevant for data storage\ , electronic and mechanical engineering\, and biomedical applications1\,2. Whereas the implementation of nanomagnetic properties into technological applications is progressing rapidly\, understanding the microscopic origin of phenomena such as magnetization enhancement or decrease\, magnetic ani sotropy and the related magnetization distribution in individual nanoparti cles\, and interparticle interactions leading to aggregation or even order ed assemblies of nanoparticles is fundamentally challenging and needs inte nsive research.\nPolarized neutrons are an excellent\, microscopic probe f or spatial and time-resolved studies of magnetism. In this contribution\, I will present examples of our recent studies of magnetic nanoparticles on different scales\, ranging from atomic magnetic structures to the mesosca le intraparticle magnetization\, and interparticle interactions in well-or dered arrays of magnetic nanocubes.\nReferences:\n[1] S. D. Bader\, Rev. M od. Phys. 78\, 1 (2006)\; DOI: 10.1103/RevModPhys.78.1\n[2] Q. A. Pankhurs t et al.\, J. Phys. D: Appl. Phys. 36\, R167 (2003)\; DOI: 10.1088/0022-37 27/36/13/201\n\nContact Person: P. v. Loosdrecht LOCATION:Seminar Room of the Institute of Physics 2 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Svetlana Mansurova DTSTART;TZID=Europe/Berlin:20171122T093000 DTEND;TZID=Europe/Berlin:20171122T113000 DTSTAMP:20260527T090435Z UID:0000001139@events.thp.uni-koeln.de DESCRIPTION:Svetlana Mansurova\, INAOE\n\nHybrid device structures based o n amorphous silicon and organic semiconductors\n\nIn the first part of the talk a brief overview of the research activities in area of fabrication a nd characterization of hybrid device structures based on amorphous silicon and organic semiconductors will be presented. The second part of the talk will be devoted to the discussion of the dynamic grating technique based on non-steady-state photo-EMF effect and its application for characterizat ion of the photo-physical properties of organic\, inorganic and hybrid sem iconductors.\n\nContact Person: Ann-Christin Schmaedicke LOCATION:Seminar Room 147\, Institute for Physical Chemistry END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Lukasz Plucinski DTSTART;TZID=Europe/Berlin:20171206T143000 DTEND;TZID=Europe/Berlin:20171206T160000 DTSTAMP:20260527T090435Z UID:0000001162@events.thp.uni-koeln.de DESCRIPTION:Lukasz Plucinski\, FZ Juelich\n\nBand structure engineering in 3D topological insulators\n\n\n\nContact Person: Alexander Grueneis LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Francois Dubin DTSTART;TZID=Europe/Berlin:20171213T143000 DTEND;TZID=Europe/Berlin:20171213T160000 DTSTAMP:20260527T090435Z UID:0000001159@events.thp.uni-koeln.de DESCRIPTION:Francois Dubin\n\nImaging the Superfluid Crossover of Trapped Two-Dimensional Dipolar Excitons\n\nState-of-the-art nano-fabrication proc ess allow to control the spatial confinement of electronic carriers\, with close to atomic precision. Structures are thus designed to separate\nspat ially oppositely charged electrons and holes\, notably bilayer heterostruc tures. When\nelectrons and hole are separated in such adjacent layers they experience a strong\nCoulomb attraction pairing them into spatially indir ect excitons\, i.e. boson-like particles\,\nwhich exhibit a giant electric dipole of about 500 Debye. Excitons then experience a\nrepulsive dipolar potential stabilizing cold gases against collapse while providing access t o\na rich variety of collective quantum phases\, possibly ranging from sup erfluidity to\nsupersolidity [1].\n\nHere\, first signatures for the super fluid crossover of such dipolar excitons are reported [2].\nWhen confined in a microscopic trap we show that they realize a four-component\nsuperflu id at sub-Kelvin temperatures\, distributed between two optically active a nd two\noptically inactive spin states. By imaging the condensate bright p art\, we study in-situ the\nprofiles of the exciton density and the phase coherence in the trap. We thus reveal\nquantum spatial coherence\, in a su b-Kelvin regime bound to very dilute densities and\nprobably limited by th e strength of dipolar interactions. Also\, we evidence quantized\nvortices \, efficiently trapped in the slight electrostatic disorder of our trappin g potential [2].\nAnalyzing the interplay between quasi long-range order\, vortex formation\, and density\nprofiles across the range of explored par ameters it is finally shown that our experimental\nfindings provide a dire ct evidence for a Berezinskii-Kosterlitz-Thouless crossover [3].\n\nThe wo rk presented here results from contributions of S.Dang\, R.Anankine\, M.Be ian\,\nM.Alloing\, E.Cambril\, A.Lemaitre and M.Holzmann.\n\nContact Perso n: Sebastian Diehl LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Igor Boettcher DTSTART;TZID=Europe/Berlin:20171220T143000 DTEND;TZID=Europe/Berlin:20171220T160000 DTSTAMP:20260527T090435Z UID:0000001181@events.thp.uni-koeln.de DESCRIPTION:Igor Boettcher\n\nComplex tensor order and quantum criticality in spin-orbit coupled superconductors\n\nA revolutionary new direction in the field of superconductivity emerged recently with the synthesis of sup erconductors with strong inherent spin-orbit coupling of electrons\, such as the half-Heusler compounds YPtBi or LuPdBi. Due to band inversion\, the low-energy degrees of freedom are electrons at a three-dimensional quadra tic band touching point with an effective spin 3/2\, which allows for Coop er pairs with spins ranging from 0 to 3. I will illuminate some of the unc onventional superconducting properties that arise from this band structure and attractive short-range interaction: (i) At strong coupling\, the syst em features an s-wave superconducting quantum critical point with non-Ferm i liquid scaling of fermions and several other unusual scaling properties. (ii) The system may further undergo a transition into a phase with comple x tensor order\, which is a superconducting state captured by a complex-va lued matrix order parameter describing Cooper pairs having spin 2. Here th e interplay of both tensorial and complex nature results in a rich and int riguing phenomenology. I will discuss the mean-field phase structure as a function of doping and temperature\, and relate our finding to experiments in YPtBi. Further\, the critical properties of this new paradigm for supe rconductivity will be addressed. \n\nContact Person: Sebastian Diehl LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Stefan Floerchinger DTSTART;TZID=Europe/Berlin:20180110T143000 DTEND;TZID=Europe/Berlin:20180110T160000 DTSTAMP:20260527T090435Z UID:0000001160@events.thp.uni-koeln.de DESCRIPTION:Stefan Floerchinger\, University of Heidelberg\n\nDynamics of entanglement in expanding quantum fields\n\nWe develop a novel real-time a pproach to computing the entanglement between spatial regions for Gaussian states in quantum field theory. The entanglement entropy is characterized in terms of local correlation functions on space-like Cauchy hypersurface s. The framework is applied to explore an expanding light cone geometry in the particular case of the Schwinger model for quantum electrodynamics in 1+1 space-time dimensions. We observe that the entanglement entropy becom es extensive in rapidity at early times and that the corresponding local r educed density matrix is a thermal density matrix for excitations around a coherent field with a time dependent temperature. Since the Schwinger mod el successfully describes many features of multiparticle production in ele ctron-positron collisions\, our results provide an attractive explanation in this framework for the apparent thermal nature of multiparticle product ion even in the absence of significant final state scattering.\n\n\nContac t Person: Sebastian Diehl LOCATION:Seminar room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Jairo Sinova DTSTART;TZID=Europe/Berlin:20180226T110000 DTEND;TZID=Europe/Berlin:20180226T123000 DTSTAMP:20260527T090435Z UID:0000001218@events.thp.uni-koeln.de DESCRIPTION:Jairo Sinova\, Mainz University\n\nTopological Antiferromagnet ic Spin-orbitronics: A Dormant Giant Awakens\n\nAntiferromagnets and ferro magnets represent two fundamental forms of magnetism with antiferromagnets being the more abundant of the two. However\, it has been notoriously dif ficult to manipulate and detect antiferromagnetic order by any practical m eans due to the compensated magnetic moment. This has left antiferromagnet s over their hundred-year history poorly explored\, in striking contrast t o the thousands of years of fascination and utility of ferromagnets. This has changed with the proposal and subsequent discovery of a new relativist ic spin-torque phenomenon\, the Neél spin-orbit torque\, that allow us to efficiently control antiferromagnetic moments in spintronic devices. This allows for antiferromagnets to become active elements in devices. An addi tional concept that has emerged is that antiferromagnets provide a unifyin g platform for realizing synergies among three prominent fields of contemp orary condensed matter physics: Dirac quasiparticles and topological phase s. These recent developments have unlocked a multitude of known and newly identified unique features of this "dormant-giant" class of materials that the community is beginning to explore.\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | . DTSTART;TZID=Europe/Berlin:20180530T140000 DTEND;TZID=Europe/Berlin:20180530T144500 DTSTAMP:20260527T090435Z UID:0000001265@events.thp.uni-koeln.de DESCRIPTION:.\n\nQM2 Members Assembly\n\n\n\nContact Person: not specified LOCATION:Seminar room Institute of Physics 2 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Markus Mueller DTSTART;TZID=Europe/Berlin:20180613T143000 DTEND;TZID=Europe/Berlin:20180613T160000 DTSTAMP:20260527T090435Z UID:0000001275@events.thp.uni-koeln.de DESCRIPTION:Markus Mueller\, Swansea University\n\nTopological Quantum Com putation: From Concepts to Experiments\n\nQuantum computers hold the promi se to allow one to solve important problems that cannot be efficiently tre ated on classical computers. To date\, the construction of a fault-toleran t quantum computer remains a fundamental scientific and technological chal lenge\, due the influence of unavoidable noise which affects the fragile q uantum states. In our talk\, we first introduce basic concepts of topologi cal quantum error-correcting color codes\, which allow one to protect quan tum information during storage and processing by distributing logical quan tum information over quantum many-body spin systems. We then discuss progr ess on experimental quantum error correction\, in particular the realisati on of a minimal topological color code with trapped ions\, which for the f irst time demonstrated basic quantum computations on an encoded logical qu bit. In the second part\, I will focus on fault-tolerant quantum computing in trapped-ion quantum processors\, in which scalability can be achieved by shuttling ions between various trapping regions and by a toolbox of io n-crystal reconfiguration techniques. I will present recent theory work of our group on resource-efficient and fault-tolerant protocols to control s ingle and coupled logical qubits of increasing size and robustness.\n\nCon tact Person: Sebastian Diehl LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Eun-Ah Kim DTSTART;TZID=Europe/Berlin:20180620T143000 DTEND;TZID=Europe/Berlin:20180620T153000 DTSTAMP:20260527T090435Z UID:0000001214@events.thp.uni-koeln.de DESCRIPTION:Eun-Ah Kim\, Cornell\n\nMachine Learning Data from Electronic Quantum Matter\n\nIn recent years\, enormous data sets have begun to appea r in real-space visualizations (scanning probes) and reciprocal-space vis ualizations (scattering probes) of electronic quantum matter. Increasing v olume and variety of such data present new challenges and opportunities th at are ripe for a new approach: machine learning. However\, the scientific questions in the field of electronic quantum matter require fundamentally new approaches to data science for two reasons: (1) quantum mechanical im aging of electronic behavior is probabilistic\, (2) inference from data sh ould be subject to fundamental laws governing microscopic interactions. In this talk\, I will review the aspects of machine learning that are appeal ing for dealing with quantum complexity and present how we implemented a m achine learning approach to analysis of scanning tunneling spectroscopy da ta.\n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Ezra Getzler DTSTART;TZID=Europe/Berlin:20180824T140000 DTEND;TZID=Europe/Berlin:20180824T153000 DTSTAMP:20260527T090435Z UID:0000001307@events.thp.uni-koeln.de DESCRIPTION:Ezra Getzler\, Northwestern University\n\nVariational calculus in the Batalin-Vilkovisky formalism and general covariance\n\nMotivated b y supersymmetry\, Batalin and Vilkovisky reformulated the equations govern ing Lagrangian mechanics in the variational calculus as a Maurer-Cartan eq uation (vanishing of curvature). This allowed them to arrive at a new unde rstanding of symmetries off-shell (i.e. where the Euler-Lagrange equation does not hold).\nIn this talk\, I will show how a modification of their Ma urer-Cartan equation can handle the action of the diffeomorphism group on the world-sheet (i.e. general covariance of the theory). Our approach invo lves the introduction of a curvature to Maurer-Cartan equation. This curva ture is central (a scalar multiple of the identity matrix) : this is analo gous to the Berry phase in the Hamiltonian approach to quantum theory (tho ugh this is really nothing more than a formal analogy).\n\nContact Person: Semyon Klevtsov LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Jae-Sung Kim DTSTART;TZID=Europe/Berlin:20180926T143000 DTEND;TZID=Europe/Berlin:20180926T160000 DTSTAMP:20260527T090435Z UID:0000001310@events.thp.uni-koeln.de DESCRIPTION:Jae-Sung Kim\, Sook-Myung Women’s University\, Seoul\n\nGrow th kinetics of Kr nano structures encapsulated by graphene\n\nGraphene can acquire salient properties by the intercalated nano structures. To functi onalize the graphene as designed\, understanding the growth kinetics of th e nano structures is a prerequisite. In that regards\, Kr atoms are select ively intercalated just below the surface graphene layer of HOPG(0001) by the incidence of low energy Kr ions. The growth kinetics of the encapsulat ed Kr nano structures is investigated by both scanning tunneling microscop y\, molecular dynamics simulations\, and the first principles calculations . \nThe intercalation proceeds via defect sites\, such as surface vacancie s. At room temperature\, the thermal diffusion of intercalated Kr is almos t frustrated despite the low diffusion barriers\, which remains as a puzzl e. The growth of Kr nano structures proceeds via the transient mobility of both the intercalating Kr atoms and previously intercalated Kr atoms that are mobilized by collision with the incident Kr ions.\nAt the elevated te mperatures where thermal diffusion becomes effective\, some Kr nano struct ures disappear\, releasing pressurized Kr atoms\, while others coalesce to form blisters via the delamination of the adjacent graphene. Some of the larger blisters explode to leave craters of varying depths at the surface. In contrast to growth on the substrate\, the growth of each encapsulated nano structure depends significantly on extrinsic variables\, such as surf ace vacancies and local topography around the nano structure\, that affect the Kr diffusion and limit the maximal Kr pressure.\n\nContact Person: Th omas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Bela Bauer DTSTART;TZID=Europe/Berlin:20181220T123000 DTEND;TZID=Europe/Berlin:20181220T140000 DTSTAMP:20260527T090435Z UID:0000001316@events.thp.uni-koeln.de DESCRIPTION:Bela Bauer\, Microsoft Research / Station Q\n\nTopologically p rotected braiding in a single wire using Floquet Majorana modes\n\nFloque t systems offer a versatile toolbox for engineering quantum phases \nthat are not allowed or at least more difficult to obtain in equilibrium \nsyst ems. A prominent example are time crystals\, which spontaneously \nbreak d iscrete time-translation symmetry. Closely related to time \ncrystals are Floquet topological phases\, such as those found in the \ndriven Kitaev ch ain. I will discuss how to perform braiding of \nnon-Abelian degrees of fr eedom - the elementary operation of topological \nquantum computation - in such a driven topological superconductor. \nUnlike the equilibrium case\, where braiding can only be performed in \ntwo-dimensional systems (or at least 2d networks of 1d systems)\, \nbraiding here is realized in a strict ly one-dimensional system\, thus \npotentially simplifying experimental de monstration.\n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christiane Koch DTSTART;TZID=Europe/Berlin:20190116T143000 DTEND;TZID=Europe/Berlin:20190116T160000 DTSTAMP:20260527T090435Z UID:0000001355@events.thp.uni-koeln.de DESCRIPTION:Christiane Koch\, University of Kassel\n\nQuantum dynamics and control for emerging quantum technologies\n\nQuantum advantage refers to exploiting the two essential elements of quantum physics\, non-locality an d coherence\, in modern technologies such as high-precision sensing or lar ge-scale computing. The actual operation of a quantum device requires a un itary operation\, and the corresponding time evolution needs to be enginee red dynamically. The desired unitaries are implemented by time-dependent e xternal electromagnetic fields. Quantum optimal control theory provides a means to derive the shape of these fields. I will discuss example applicat ions of optimal control theory from quantum sensing and quantum computing and I will show how suitably shaped pulses reach maximum fidelity in minim um time\, despite the presence of losses and imprecision.\n\nContact Perso n: Tommaso Calarco LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Arkady Fedorov DTSTART;TZID=Europe/Berlin:20190117T143000 DTEND;TZID=Europe/Berlin:20190117T160000 DTSTAMP:20260527T090435Z UID:0000001370@events.thp.uni-koeln.de DESCRIPTION:Arkady Fedorov\, University Queensland\n\nSuperconducting quan tum circuits for waveguide quantum electrodynamics (QED)\n\nSuperconductin g quantum circuits are artificial structures with a possibility to enginee r their key parameters by design and fabrication. Moreover\, many of these parameters can be in-situ tuned during experiments. These attractive prop erties have made superconducting circuits an ideal platform for quantum en gineering such as quantum information processing and quantum optics on a c hip. In this talk\, I will underline the main physical mechanisms of these systems and will focus on benefits of the superconducting devices for wav eguide quantum electrodynamics (QED)\, a regime where one or several quant um emitters are coupled strongly to a continuum of electromagnetic modes i n one dimension. I will show that a basic ingredient of waveguide QED\, a single qubit in a waveguide\, behaves as a mirror with its transparency de pending on the frequency and power of the incoming radiation. I will then show that when two qubits are inserted in a waveguide one can observe addi tional cooperative effects dependent on the distance between the qubits. F inally\, I will outline how these non-local cooperative interactions can b e used to create non-reciprocal transmission\, distribute entanglement and generate new physical regimes of light-matter interaction.\n\nContact Per son: Alexander Grüneis LOCATION:Seminarraum alte Theorie END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Johannes Kellendonk DTSTART;TZID=Europe/Berlin:20190521T101500 DTEND;TZID=Europe/Berlin:20190521T114500 DTSTAMP:20260527T090435Z UID:0000001417@events.thp.uni-koeln.de DESCRIPTION:Johannes Kellendonk\, Institut Camille Jordan (Lyon)\n\nThe bu lk boundary correspondence for quasiperiodic chains\n\nAlmost periodic cha ins (models for incommensurate phases) and\nquasiperiodic chains (models f or quasicrystals) have a richer\ntopological phase structure than periodic chains\, due to the existence\nof phasons. This effects the bulk boundary correspondence for these\nmodels. We investigate in particular quasiperio dic chains where the\nphason degree of freedom lives in a totally disconne cted space. We show\nhow we can nevertheless define a winding number for t he boundary\nresonances and thus obtain an equation which relates the inte grated\ndensity of states at a gap to a winding number which can be interp reted\nas the work the phason motion exhibits on the edge states of the sy stem.\n\nContact Person: Christopher Max LOCATION:Stefan Cohn‐Vossen Raum des Mathematischen Instituts (Raum 313) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | A/P Dane Mc Caney DTSTART;TZID=Europe/Berlin:20190628T140000 DTEND;TZID=Europe/Berlin:20190628T153000 DTSTAMP:20260527T090435Z UID:0000001430@events.thp.uni-koeln.de DESCRIPTION:A/P Dane Mc Caney\, UNSW Sydney\n\nSpins in Organic Optoelectr onic Materials and Devices\n\nSpin plays a central role in a wide range of optoelectonic processes in organic materials and devices. I will introduc e electrical and optical detection schemes for electron spin resonance (E SR)\, which can be used to probe the Optoelectronic properties of organic electronic devices. I will then discuss results of ESR experiments on mat erials for singlet fission\, electrical and optical detection of ESR in or ganic light emitting diodes\, and correlations between ESR and magnetolumi nescence and magnetoconductivity experiments in OLEDs.\n\nContact Person: Ann-Christin Schmaedicke LOCATION:Seminar room 147 (Basement hall at Physical Chemistry\, Departmen t of Chemistry) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Paul Wiegmann DTSTART;TZID=Europe/Berlin:20190708T143000 DTEND;TZID=Europe/Berlin:20190708T160000 DTSTAMP:20260527T090435Z UID:0000001416@events.thp.uni-koeln.de DESCRIPTION:Paul Wiegmann\, University of Chicago\n\nQuantization of hydro dynamics and gravitational anomaly\n\nI will present a consistent scheme o f quantization of chiral flows (flows with extensive vorticity) in ideal h ydrodynamics in two dimensions. Chiral flows occur in rotating superfluid\ , rotating turbulence and also in electronic systems in the magnetic field in the regime of a fractional Hall effect. The quantization is based on a geometric relation of chiral flows to two-dimensional quantum gravity and is implemented by the gravitational anomaly. The effect of the gravitatio nal anomaly violates the major property of classical hydrodynamics\, the H elmholtz law: vortices are no longer frozen into the flow. Effects of quan tization could be cast in the form of quantum stress. I show that the quan tum stress generates Virasoro algebra\, the centrally extended algebra of holomorphic diffeomorphisms.\n\nContact Person: Semyon Klevtsov LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | S.A. Jafari DTSTART;TZID=Europe/Berlin:20190717T143000 DTEND;TZID=Europe/Berlin:20190717T160000 DTSTAMP:20260527T090435Z UID:0000001381@events.thp.uni-koeln.de DESCRIPTION:S.A. Jafari\, Sharif University of Technology\n\nSolid state s ystems with deformed Minkowski spacetime\n\nContinuum limit of Dirac solid s can be described as a Minkowski \nspacetime. Certain nonsymmorphic 2D la ttices host tilted Dirac fermions.\nThe effective spacetime felt by these electrons is a deformation of Minkowski\nspacetime where temporal and spat ial affairs are mingled. In this talk\, first we\nuse irreducible represen tations of the 8Pmmn borophene to show that not only \nthe resulting space time is the tilt deformation of Minkowski spacetime\, but also \nthe resul ting tilt can be manipulated by a perpendicular electric field. We discuss \nunusual plasmons and electromagnetic response of 2D tilted-Dirac cone s olids.\n\nContact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Joel D. Cox DTSTART;TZID=Europe/Berlin:20191127T143000 DTEND;TZID=Europe/Berlin:20191127T160000 DTSTAMP:20260527T090435Z UID:0000001468@events.thp.uni-koeln.de DESCRIPTION:Joel D. Cox\, University of Southern Denmark\n\nNonlinear Grap hene Nanoplasmonics\n\nNonlinear optics is limited by the weak nonlinear r esponse of available materials\, a problem that is generally circumvented by relying on macroscopic structures in which light propagates over many o ptical cycles\, thus giving rise to accumulated unity-order nonlinear effe cts. While this strategy cannot be extended to subwavelength optics\, one can alternatively use localized optical resonances with high quality facto rs to increase light-matter interaction times at the expense of inelastic losses associated with the nonlinear response. In this context\, highly-do ped graphene has been identified as a promising material platform for nonl inear optics that combines long-lived\, electrically-tunable plasmons with an intensely anharmonic response to light originating from its unique ele ctronic band structure. I will discuss recent progress in the exploration of nonlinear graphene plasmonics\, starting with a description of the appe aling properties of plasmons in graphene nanostructures down to molecular sizes\, followed by a discussion of the unprecedented level of intrinsic o ptical nonlinearity in graphene and its enhancement by resonant coupling t o its supported plasmons of high harmonic and Kerr nonlinearities\, strong interactions of nonlinear plasmons with quantum emitters or amongst thems elves\, and the extraordinary thermo-optical capabilities of this material enabling nonlinear optical switching on the single-photon level.\n\nConta ct Person: Klas Lindfors LOCATION:lecture hall III (chemistry building) END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Christian Papp DTSTART;TZID=Europe/Berlin:20210120T143000 DTEND;TZID=Europe/Berlin:20210120T153000 DTSTAMP:20260527T090435Z UID:0000001584@events.thp.uni-koeln.de DESCRIPTION:Christian Papp\, Friedrich-Alexander-Universität Erlangen-Nü rnberg\n\nNanocluster arrays: from model catalysis to nanographene\n\nThe talk will cover spectroscopic investigations on the catalytic properties o f iron nanoparticle arrays and details on the formation of nanographene in nano-heterostructures. \nThe increased complexity of real-life catalysts as compared to surface science leads to the “materials gap”. To close this gap\, studies of adsorption and reaction experiments on nanoparticles supported on 2D materials were conducted under in situ conditions with th e particular aim to elucidate the reactivity of such more “realistic” nanoparticles. It is shown that the use of a quantitative spectroscopy all ows for gaining a detailed insight even to these complex systems\, thereby facilitating a further step into bridging the materials gap from fundamen tal science to applied sciences. The use of the 2D materials as a chemical ly “innocent” substrate gives the intriguing possibility to study the system without the additional influence of side processes such as spill ov er and reverse spill over. Such studies allow for characterization of nove l cluster systems towards their reactivity and adsorption behavior\, e.g. for iron nanoclusters with the probe molecule CO. Such reactivity studies are also possible for the more complex chemistry of ethylene on Pt nanoclu sters where detailed insights to the reaction pathway become available. Th ereby the changes when going from single crystals to nanoclusters become e vident. \nAs a second topic\, the formation of van-der-Waals nano-heterost ructures is discussed. Insights from spectroscopic and microscopic studies allowed us to characterize the individual preparation steps and the final nano-heterostructure consisting of graphene / metal / h-BN stack. Experim ents with different cluster sizes are shown to obtain insights to the pore filling of the h-BN substrate. This gives a direct measure of the agglome ration of the nanoclusters during preparation. \n\nLiterature \nF. Düll\ , et al. ACS Applied Nano Materials 2 (2019) 7019.\nF. Düll\, et al. Jour nal of Chemical Physics 152 (2020) 224710.\nF. Düll\, et al. Physical Che mistry Chemical Physics 21 (2019) 21287.\n\nContact Person: Pantelis Bampo ulis LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Alec Wodtke DTSTART;TZID=Europe/Berlin:20210127T143000 DTEND;TZID=Europe/Berlin:20210127T160000 DTSTAMP:20260527T090435Z UID:0000001586@events.thp.uni-koeln.de DESCRIPTION:Alec Wodtke\, Max Planck Institute for Biophysical Chemistry\, Göttigen\n\nExperiments on vibrational energy pooling and transport in c ondensed phases using a mid-ir superconducting nanowire single photon dete ctor\n\nSuperconducting nanowire single-photon detectors (SNSPDs) provide sufficient sensitivity to enable laser induced fluorescence (LIF) experime nts in the mid-infrared\, an exciting technical development for physical c hemistry given the importance of vibrational spectroscopy to molecular sci ence. In this talk\, I will describe how an SNSPD works and how to use it. I will also present results of experiments on the vibrational dynamics of monolayers and multilayers of solid CO adsorbed at the surface of a NaCl crystal\, to show the capabilities of time-resolved infrared LIF spectrosc opy and provide observations of astonishing phenomena arising from dipole- dipole coupling between molecules.\nIn these experiments\, a laser light p ulse excites about half of the CO to its \n\nContact Person: Thomas Michel y LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Boris Senkovskiy DTSTART;TZID=Europe/Berlin:20210210T143000 DTEND;TZID=Europe/Berlin:20210210T160000 DTSTAMP:20260527T090435Z UID:0000001590@events.thp.uni-koeln.de DESCRIPTION:Boris Senkovskiy\, Physics Institute II\n\nElectronic band str ucture and optical properties of mechanical stacked heterostructures of 2D semiconductors\n\n\n\nContact Person: Boris Senkovskiy LOCATION:Zoom: https://us04web.zoom.us/j/77633503456?pwd=bzNZZmJOcENnVmZpb XAycXAzc3oxUT09 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dr. Monika Schied - University of Graz DTSTART;TZID=Europe/Berlin:20211015T143000 DTEND;TZID=Europe/Berlin:20211015T153000 DTSTAMP:20260527T090435Z UID:0000001658@events.thp.uni-koeln.de DESCRIPTION:Dr. Monika Schied - University of Graz\n\nMolecular Motors on Surfaces Studied by Scanning Tunnelling Microscopy\n\nArtificial molecular motors that convert external energy into controlled motion have seen grea t developments in the last decades [1]. While many studies exist in soluti on\, little is known how such functional molecules behave on a surface. Ho wever\, such a solid support can be advantageous as it offers fixed points of reference as well as confinement in two dimensions\, making it easier to study the directionality of their motion.\nWe have studied so-called Fe ringa motors on various surfaces by low-temperature scanning tunnelling mi croscopy (STM). On Cu(111) these molecules adsorb in three different confo rmations\, which are related to the states of the motor cycle in solution. The relative stability of the in-solution motor states is reversed on the surface. It was found that rotations of individual molecules can be induc ed over rather long distances up to about 100 nm by voltage pulses with th e STM tip. Importantly\, these rotations show high directionality (clockwi se or anticlockwise)\, which will be discussed in view of their specific c hemical structure and adsorption. [1] W. R. Browne and B. L. Feringa\, Nat . Nanotech. 1\, 25 (2006)\n\nContact Person: Thomas Michely LOCATION:Hörsaal 2 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | John Lupton DTSTART;TZID=Europe/Berlin:20220518T170000 DTEND;TZID=Europe/Berlin:20220518T183000 DTSTAMP:20260527T090435Z UID:0000001730@events.thp.uni-koeln.de DESCRIPTION:John Lupton\, Department of Physics\, University of Regensburg \n\nOLED Magnetoreception\n\n\n\nContact Person: not specified LOCATION:Kurt-Alder lecture hall\, Department of Chemistry END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Prof. Jani Kotakoski / Universität Wien DTSTART;TZID=Europe/Berlin:20220622T160000 DTEND;TZID=Europe/Berlin:20220622T170000 DTSTAMP:20260527T090435Z UID:0000001735@events.thp.uni-koeln.de DESCRIPTION:Prof. Jani Kotakoski / Universität Wien\n\nNew materials and nanostructures via graphene substrates and van der Waals sandwiches\n\nGra phene--the one-atom-thick sheet of carbon--is the most famous of 2D materi als due to its unique electronic properties and mechanical strength. Howev er\, its chemical inertness makes graphene also an excellent nearly electr on-transparent support for other materials and nanostructures. In this pre sentation\, I will give an overview of our recent work enabled by a unique interconnected vacuum system containing an aberration-corrected scanning transmission electron microscope (Nion UltraSTEM 100) with a unique object ive area that allows sample cleaning via laser\, in situ chemical experime nts\, and direct vacuum transfer to an atomic force microscope (AFSEM by G eTEC Microscopy)\, an argon glove box\, target chamber with a plasma ion s ource and evaporators\, and long term vacuum sample storage. In this prese ntation\, I will demonstrate that defect-engineering of graphene enables i ts substitutional heteroatom doping and growth of nanoclusters with a well -defined concentration and a narrow size distribution\, as well as the dir ect correlation of its atomic structure and mechanical properties.\n\nCont act Person: Thomas Michely LOCATION:Raum 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Jeonghun Kwak DTSTART;TZID=Europe/Berlin:20230810T110000 DTEND;TZID=Europe/Berlin:20230810T123000 DTSTAMP:20260527T090435Z UID:0000001873@events.thp.uni-koeln.de DESCRIPTION:Jeonghun Kwak\, Seoul National University\n\nQuantum dot light -emitting diodes: Fundamentals and application for future displays\n\nQuan tum dot (QD) light-emitting diodes (QLEDs) are considered one of the most promising devices for future full-colour displays due to their high colour purity with narrow emission bandwidth\, high brightness\, and solution pr ocessability. However\, fundamental mechanisms\, such as charge injection into QDs\, exciton recombination\, and operational stability\, should be u nderstood to realise the QLED displays. Here\, we present the recent resea rch progress in our group to unravel the mechanisms of charge carrier and exciton dynamics in QLEDs\, and the device design and fabrication processe s to achieve high performance QLEDs.\n\nContact Person: Andreas Sindermann LOCATION:Chemie HS III END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Prof. Steven de Feyter DTSTART;TZID=Europe/Berlin:20230907T140000 DTEND;TZID=Europe/Berlin:20230907T153000 DTSTAMP:20260527T090435Z UID:0000001877@events.thp.uni-koeln.de DESCRIPTION:Prof. Steven de Feyter\, KU Leuven\, Belgium\n\nFormation and functionalization of 2D materials: a molecular approach\n\nIn this present ation\, I will mainly focus on the functionalization of graphite\, graphen e\, and transition metal dichalcogenides using molecules\, though the conc epts can be applied to other 2D materials too. Nanostructuring is at the h eart of all functionalization protocols that we develop because it opens n ew possibilities for control and functionality. A variety of scanning prob e microscopy methods are used for visualization\, characterization\, and m anipulation. The first approach is based on molecular self-assembly at the interface between a liquid or air\, and graphite or graphene. A second ap proach is based on the covalent attachment of molecules on 2D materials vi a covalent chemistry. It will be demonstrated how in addition to bottom-up strategies that provide control on the density and layer thickness\, as w ell as submicron to nanoscale nanostructuring\, also top-down scanning pro be microscopy and optical lithography can be used to structure such covale ntly modified surfaces. A third approach does not focus on the functionali zation of the surface\, but uses the surface as a support for the in-plane covalent stitching of molecules\, leading to the formation of on-surface 2D dynamic covalent polymers.\n\nContact Person: Hanna Krikcziokat LOCATION:Exp. Sem. 1\, Chemistry Department END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dr. Marcel Rost DTSTART;TZID=Europe/Berlin:20240417T143000 DTEND;TZID=Europe/Berlin:20240417T160000 DTSTAMP:20260527T090435Z UID:0000001930@events.thp.uni-koeln.de DESCRIPTION:Dr. Marcel Rost\, Universität Leiden\, NL\n\nSurprising Aspec ts during Electrochemical Pt(111) Oxidation and Reduction: Unravelling Dif ferent Oxidation Stages\n\nRepeated oxidation and reduction of a platinum electrode\, which can be compared to the switching ON and OFF of a device (e.g. fuel cell\, electrolyzer\,…)\, leads to the roughening of the surf ace\, caused by the nucleation and growth of nano-islands\, which first gr ow only laterally (2D) and then exclusively in height (3D). Surprisingly\, this particular nucleation and growth combines several remarkable aspects that all deviate from standard text book- and literature-knowledge. The b asic mechanism is rooted in the larger lattice constant of platinum-oxide such that the growth is promoted by the creation of adatoms and vacancies\ , implying that not only growth processes but also etching processes have to be considered.\n\nIt is remarkable that the nano-islands arrange in an almost perfect\, hexagonal pattern\, which clearly deviates from standard random growth. Surprisingly\, many other chemical surface systems develop highly ordered nano-islands during cycles of surface reaction and restorat ion. In the case of platinum the nano-islands growth eventually enhances t he dissolution\, which makes electrochemical energy applications\, like in fuel cells and electrolysers\, economically less feasible\, as it is scar ce and expensive. Preventing nucleation would be most effective for preven ting roughening. However\, little is known about the atomic details regard ing the nucleation\; a process almost impossible to observe.\nI will show that platinum exhibits four different (pre-)oxidation stages that are resp onsible for the mysterious observations\, all leading to very peculiar ato mic changes and surface structures\, before real bulk oxidation occurs. Fi rst the adatoms of the surface-background adatom gas are oxidized\, but th e equilibrium adatom pressure shoots up simultaneously such that nucleatio n does not occur during the oxidation\, where the atoms are created and pu shed on top of the surface. Surprisingly\, they nucleate during the reduct ion. Secondly\, analysing the island distance-distribution\, we derive a r arely observed non-random nucleation\, which can only occur if there is a repulsive interaction between the depositing atoms or the existence of pre ferential nucleation sites. Fundamentally interesting\, as never observed before\, we do show that special\, preferential nucleation sites that a pr iori do not exist\, develop initially via a precursor and eventually form a semi-ordered Pt-oxide structure: the famous spoke wheels\, which are ass embled from Pt atoms that exchanged their places with oxygen atoms going s ubsurface. At low coverages the system is fully reversible and restores up on reduction. We can model the reversible place exchange coverage with a F rumkin isotherm combined with an Arrhenius diffusion term. At high coverag es irreversible place exchange atoms are created that are pushed onto the Pt(111) surface\, leading eventually to the ordered nano-islands.\nInteres tingly\, the pre-oxidation stages are expected to occur also on many other surfaces during oxidation and nano-islands growth has been reported befor e also on Cu\, Ag\, and Au. We expect similar precursors and pre-stages to form also during nitride and sulfide formation.\n\nContact Person: Thomas Michely\, Matteo Cacco LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Hidetoshi Nishimori DTSTART;TZID=Europe/Berlin:20240515T160000 DTEND;TZID=Europe/Berlin:20240515T170000 DTSTAMP:20260527T090435Z UID:0000001969@events.thp.uni-koeln.de DESCRIPTION:Hidetoshi Nishimori\, Tokyo Institute of Technology\n\nError c orrection in the Lechner-Hauke-Zoller scheme for quantum annealing\n\nErro r correction plays a crucial role in quantum computing to obtain reliable results from noisy devices. I will begin by reviewing the spin glass theor y based on gauge symmetry. Interestingly\, this theory is formally equival ent to Bayes inference in classical error-correcting codes. Then\, I will introduce the Lechner-Hauke-Zoller scheme for quantum annealing and demons trate that a simple majority vote of syndromes extracted from this scheme is Bayes-optimal for error correction. Work done in collaboration with Yos hihiro Nambu.\n\nContact Person: Guo-Yi Zhu / Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Dr. Jiawei Shen DTSTART;TZID=Europe/Berlin:20240815T140000 DTEND;TZID=Europe/Berlin:20240815T150000 DTSTAMP:20260527T090435Z UID:0000002020@events.thp.uni-koeln.de DESCRIPTION:Dr. Jiawei Shen\, Hangzhou Normal University\, China\n\nStudy on the Growth Mechanism of Crystals on Liquid Substrates\n\nFabrication of high-quality crystals via environmentally friendly and efficient processe s has been a long-standing issue in the field of crystal growth. Here\, we extend a general preparation method of nanostructures\, which makes it po ssible to synthesize crystals on liquid substrates. In this topic\, the re search progress made in recent years are introduced. Then the general prep aration methods\, the formation mechanism of the crystals on liquid substr ates (for instance\, the growth mechanism of graphene\, nanotube\, and mol ybdenum disulfide\, etc.) and the advantages of using liquid substrates to prepare various low-dimensional crystals are presented and discussed. The se research advances will provide experimental and theoretical basis for t he subsequent preparation of various crystals on liquid substrates.\n\nCon tact Person: Thomas Michely LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Sergey Streltsov DTSTART;TZID=Europe/Berlin:20240918T150000 DTEND;TZID=Europe/Berlin:20240918T160000 DTSTAMP:20260527T090435Z UID:0000002025@events.thp.uni-koeln.de DESCRIPTION:Sergey Streltsov\, Institute of Metal Physics\, Ural Federal U niversity\, RU\n\nThree stories of unusual magnetism: Kitaev pyroxene SrCo Ge2O6\, Kagome magnets YMn6Sn6 and LiZn2Mo3O8\n\nThree quite different mat erials exhibiting unusual magnetic and electronic properties will be discu ssed in the talk. \n\nWe start with pyroxenes - SrCoGe2O6. This class of m aterials have been actively investigated in University of Cologne and our recent finding\, that the Kitaev physics is relevant for Co-based pyroxene s can be interesting for the audience. Then\, we will discuss Kagome magne t YMn6Sn6\, which in additional to famous flat bands in electronic spectru m demonstrates the orbital-selective behaviour\, which in turn explains it s magnetic properties. We conclude with an interesting class of materials with a breathing Kagome – Nb3Cl8 and AxByMo3O8\, which depending on choi ce of B (B=Sc\, Zn\, In) and A (A=Li\,Na\,Zn) ions have very different mag netic properties – they can be not only both antiferro- or ferromagnets\ , but in some of them the long-range magnetic order turns out to be suppre ssed and a mysterious spin-liquid state (possibly associated with a plaque tte charge order) or non-magnetic ground stats can be realized in these sy stems.\n\nThe work is supported by the grant RSF 23-12-00159.\n\nContact P erson: Markus Braden / Matteo LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:QM2 | Karl-Heinz Ernst DTSTART;TZID=Europe/Berlin:20241024T170000 DTEND;TZID=Europe/Berlin:20241024T180000 DTSTAMP:20260527T090435Z UID:0000002066@events.thp.uni-koeln.de DESCRIPTION:Karl-Heinz Ernst\, EMPA\, Zürich\n\n(TIDE-Kolloquium) Chirali ty in Flatland: Magneto-Chiral Selectivity\, Topological Self-Assembly and Molecular Motoring of Helical Aromatics on Surfaces\n\nSoon after his sem inal discovery of molecular chirality Pasteur suggested physical fields as its origin and assumed that magnetic fields must be the source of chirali ty in the universe. Lord Kelvin refuted Pasteur's suggestions and made cle ar that magnetism has no chirality. In 1894\, Pierre Curie proposed that p arallel and antiparallel alignments of electric and magnetic fields will i nduce chirality\, but such chiral influence must vanish under conditions o f thermodynamic equilibrium. We report that single helical aromatic hydroc arbons\, so-called helicenes\, undergo enantioselective adsorption on ferr omagnetic cobalt surfaces. Spin- and chirality sensitive scanning tunnelin g microscopy (STM) reveals that molecules of opposite handedness prefer ad sorption onto cobalt islands with opposite out-of-plane magnetization. As mobility ceases in the final chemisorbed state\, it is concluded that enan tioselection must occur in a physisorbed transient precursor state. Such o bservation suggests electron spin-depend van-der-Waals forces. Simultaneou s measurements of the tunneling current through both enantiomers on a give n Co nanoisland yields a magneto-chiral specific conductance of up to 50% for single helicene molecules\, thus refuting previously proposed ensemble effects as origin of the so-called chirality-induced spin selectivity (CI SS). Our results open the opportunity towards new single-molecule spin-val ve devices and shine light into the origin of CISS. Finally\, the first su ccessful electrical current-driven unidirectional motion of a synthetic mo lecule\, the so-called nanocar\, will be presented and compared to recent results obtained for smaller molecular machines propelled by inelastic ele ctron tunneling.\n\nContact Person: Klaus Meerholz LOCATION:OTHER END:VEVENT END:VCALENDAR