Effects of strong electron correlations in X-ray and electron spectra of high-T-c superconductors

The current state of theoretical and experimental studies on the electronic structure of high-T-c superconductors is analyzed. The agreement between t he theory and experimental spectroscopic data is shown to be rather poor in certain cases. The reason is that the X-ray and electronic spectra reveal strong electron correlations. At the same time, no realistic model has been developed up to now in which both one-electron and multielectron mechanism s of the formation of the spectra could be described in a unified way in co mpounds containing transition and rare-earth elements. In this paper, parti cular attention is paid to a sudden-perturbation model, by which it has bee n possible to describe or interpret some X-ray and electronic spectra, incl uding both one-electron and multielectron effects. (C) 2000 MAIK "Nauka/Int erperiodica".