Electron-phonon coupling in metallic systems - Self energy and superconductivity

Friedrich Theodor Reinert

Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

By use of high-resolution analysers one has become able to investigate in detail the influence of many-body interactions on the photoemission spectra of solids. Electron-phonon coupling leads for example to a temperature dependence of the photoemission linewidth, from which one can determine the coupling parameter lambda. Recently it has been shown for several simple metallic systems (in particular surface states), that even the slight change of the band dispersion near the Fermi level can be observed experimentally. This change is closely related to the energy dependence of the photoemission linewidth on the same energy scale. The quantitative analysis of the dispersion and the linewidth allows an immediate comparison with the real and the imaginary part of the electron-phonon self energy, respectively, as given by comparatively simple models, like the Debye model, or by ab initio calculations. In the case of superconductors, one can try compare these results, obtained above the transition temperature, with the details of the photoemission spectra in the superconducting phase. A possibly consistent description of the spectra above and below the transition temperature can give important information about the superconducting coupling mechanism.