QM2 - Quantum Matter and Materials | July 09, 14:30
“Edge science”: electronic states in geometrically and electronically confined surface structures
Fascinating 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 fabricated by lithography and self-assembly, respectively, where the spectroscopic signatures and transport properties are determined by their edges and step structures: Pb adsorbed on Si(557) leads to formation of long range ordered quantum wire ensembles. At temperatures below 78K the system undergoes a refacetting transition accompanied by a metal-insulator transition. The insulating behavior found in the direction across the wires can be explained in terms of Fermi nesting [1]. Recently, the spin-orbit coupling in this system and its impact to magneto-transport measurements have been analyzed in detail. The spin polarization of the Fermi surface, manifested already in the suppression of spin-orbit coupling along the wires within the 1D transport regime, has been confirmed by spin-resolved ARPES measurements. The magnitude of the Rashba-splitting in this strongly anisotropic system evidences the formation of a spin density wave, which is the ground state of a CDW system electron-electron interaction [2]. The regime of mesoscopic transport physics has been entered with graphene nanoribbon structures (GNR) grown on SiC-MESAs. By means of a 4-tip STM/SEM system ballistic transport channels with mean free path lengths up to 10 µm at room temperature have been identified [3]. The existence of edge-localized states near the zig-zag edges have been confirmed by first STS spectra taken across the ribbon [4]. [1] C. Tegenkamp, et.al. PRL 95, 176804 (2005) [2] C. Tegenkamp, et.al. PRL 109, 266401 (2012) [3] J. Baringhaus ,et.al., Nature 506, 349 (2014) [4] J. Baringhaus et.al. JPCM, 25, 392001 (2013).
Christoph Tegenkamp, Universität Hannover
Seminar Room of the Institute of Physics II (R201)
Contact: Carsten Busse