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M: Metallphysik
M 30: Elektronische Eigenschaften
M 30.1: Fachvortrag
Donnerstag, 29. März 2001, 17:15–17:30, S5.3
Photoemission lineshape at finite temperature — •Ph. Hofmann1, Ch. Søndergaard1, Ch. Schultz1, S. Moreno2, J.E. Gayone2, M.A. Vincente Alvarez2, G. Zampieri2, S. Lizzit3, and A. Baraldi3 — 1Institute for Storage Ring Facilities, University of Aarhus, 8000 Aarhus C, Denmark — 2Centro Atómico Bariloche and Instituto Balseiro, Commisión Nacional de Energía Atómico, 8400-Bariloche, Argentina — 3Sincrotrone Trieste S.C.p.A, 34012 Trieste, Italy
We have measured angle-resolved photoemission spectra from Al(001) over a large range of temperatures and photon energies. This data was analyzed using a model that allows to calculate the photoemission intensity for transitions with the simultaneous excitation/absorption of 0, 1, 2, etc. phonons. We show that the so-called direct transition (or quasiparticle) peaks always contain a significant contribution from photoemission events with a simultaneous excitation and/or absorption of 1 and 2 phonons, i.e. from transitions which are actually indirect. At low photon energies and/or low temperatures these contributions are small; but as the photon energy or the temperature is raised they increase relative to the elastic or zero-phonon contribution and eventually become the dominant contribution to the so-called direct transition peak. The effect of these phonon-assisted transitions is a significant change of the photoemission lineshape. Our model gives a good description of the temperature dependence in the experimental data but only if the phonon-assisted contributions to the photoemission peak are taken into account.