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O: Oberflächenphysik

O 35: Hauptvortrag

O 35.1: Invited Talk

Friday, March 31, 2000, 09:30–10:15, H36

Photoemission studies of unconventional electron systems — •Yves Baer — Universite de Neuchatel, Institue de Physique, Rue A.-L. Breguet 1, CH-2000 Neuchatel

Photoemission at low energy is certainly one of the most powerful and straightforward tool to probe the electronic states in solids. Numerous studies have demonstrated that a gratifying agreement is found between photoemission data and single-particle band calculations. However, many-body mechanisms can markedly obscure this simple analysis and require an interpretation in terms of quasi-particles which are reminiscent of independent particles. This aspect will be illustrated by a study of the surface electronic state on Be(0001) which shows an exceptionally strong coupling with the phonons. A complete breakdown of the quasi-particle concept occurs in one-dimensional metals where the spectral functions calculated within the Luttinger liquid model contain distinct excitations of spin and charge collective modes (spinons and holons). By Au deposition on a vicinal surface of Si(111) we have prepared single-atom metallic chains approaching ideal conditions of one dimensionality. Their photoemission spectra display an explicit hint of separated spin and charge excitations.