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For a long time, rare-earth (RE) intermetallic materials have attracted considerable interest be-cause of their exotic properties at low temperatures which include complex magnetic phases, valence fluctuations, heavy-fermion states, Kondo behavior and many others. It is widely believed that all of these properties stem from the delicate interplay between almost localized 4f electrons and itinerant valence band states. Our experiments aim to disclose details of this interaction, and reveal the fine electronic struc-ture of such materials near the Fermi level. To this end, we apply Angle-Resolved Photoemission Spectroscopy (ARPES) technique, which in spite of its surface sensitivity when working in UV mode, indeed, allows to gain deep insight not only into surface electron structure, but to probe the bulk de-rived states, too. In that regard, the particular point of our experiments is the proper discrimination of (sub-) surface and bulk related phenomena. In the past years we performed extensive ARPES studies on the RERh2Si2 (RE = Ce, Eu and Yb) series of compound as well as on YbIr2Si2 With our approach we were able to address some of the topics at the core of strongly correlated 4f electron systems: (i) observation of crystal-electric field (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 reflecting f-d coupling at the surface and bulk of the material. Studying its temperature dependence for a Kondo lattice (YbRh2Si2); (iii) clear evidence of the interplay of Dirac fermions and heavy quasi-particles; (iv) manifestation of unusual and strong ferromagnetism at the Si-terminated surface of an antiferromagnet (EuRh2Si2) caused by buried 4f magnetic moments of Eu lying 4-layers below the surface. [1] A. Chikina et al., Strong ferromagnetism at the surface of an antiferromagnet caused by buried magnetic moments, Nature Communications 5, 3171 (2014). [2] M. Höppner et al., Interplay of Dirac fermions and heavy quasiparticles in solids, Nature Commu-nications 4, 1646 (2013). [3] S. Danzenbächer et al., Insight into the f-derived Fermi surface of the heavy-fermion compound YbRh2Si2, Phys. Rev. Lett. 107, 267601 (2011). [4] D.V. Vyalikh et al., k-dependence of the crystal-field splittings of 4f states in rare-earth systems, Phys. Rev. Lett. 105, 237601 (2010). [5] D.V. Vyalikh et al., Tuning the hybridization at the surface of a heavy-fermion system, Phys. Rev. Lett., 103, 137601 (2009).

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Denis Vyalikh, Institute of Solid State Physics, University of Technology Dresden, D-01062 Dresden, Germany
Seminar Room of the Institute of Physics II (R201)
Contact: Alexander Grueneis