Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 2: Invited Talk Marco Grioni: Broken Symmetry States at Surfaces: The ARPES View
O 2.1: Hauptvortrag
Montag, 26. März 2007, 09:30–10:15, H36
Broken symmetry states at surfaces: the ARPES view — •Marco Grioni — IPN-EPFL, Lausanne, Switzerland
The surface of a solid may exhibit electronic phases that break a symmetry present in the material’s bulk. Photoelectron spectroscopy (ARPES) with high energy and momentum resolution can probe the properties of such electronic states with a rather unique sensitivity and selectivity. Here I will briefly discuss two such examples. Peculiar surface structures result from qualitatively different mechanisms: enhanced surface correlations in the former, and the genuine breaking of an underlying symmetry in the latter.
In the layered materials 1T-TaSe2 the interplay of temperature-dependent charge-density-waves (CDW) and electronic correlations yields a bandwidth-controlled metal-insulator surface transition on top of a metallic bulk. ARPES reveals the breakdown of the Fermi surface and the disappearance of the coherent quasiparticle weight.
In the epitaxial PbAg2 alloy formed at the Ag(111) surface, the breaking of inversion symmetry in the presence of spin-orbit interaction lifts the Kramers’ spin degeneracy, and states of opposite spin are separated in momentum. The giant splitting (Δ k = ± 0.13 Å) observed by ARPES cannot be explained by a standard free-electron (Rashba-Byckhov) model, and points to the crucial role played by the formation of the chemical bonds.