EFFECTS OF ELECTRON CORRELATIONS ON AUGER-ELECTRON AND APPEARANCE-POTENTIAL SPECTRA OF SOLID-SURFACES

In the past the Cini-Sawatzky model and its generalizations to arbitra ry band-filling and orbital degeneracy have been employed extensively in the discussion of electron-correlation effects in CVV Auger-electro n (AE) and appearance-potential (AP) spectra of solid surfaces. In all these attempts, however, the strong inherent perturbation of the vale nce-band system due to the core-hole potential has been neglected up t o now. We present results of a new theoretical approach for arbitrary band-filling, which for the first time accounts for the on-site Coulom b interaction among the valence-band electrons U and for the Coulomb i nteraction between valence-band and core electrons U(c) as well. The A E- and AP-intensities are given by a three-particle Green function, wh ich is calculated using a diagrammatic vertex-correction method. The s pectra show a strong dependence on the valence-band-core interaction U (c) and exhibit several satellite features in the strong-correlation c ase. They indicate the importance of an accurate description of the ef fects of the core-hole potential for AE- and AP-spectra of solids.