THEORY OF AUGER-ELECTRON AND APPEARANCE-POTENTIAL SPECTROSCOPY FROM SOLIDS WITH PARTIALLY FILLED VALENCE BANDS - EFFECTS OF VALENCE-BAND CORE INTERACTION

Abstract

CVV Auger electron and appearance-potential spectra of solids are well known to exhibit strong satellite features depending on the ratio of on-site Coulomb interaction among the valence-band electrons U and the width of the free Bloch band W. We present a theory that additionally includes the effects of the Coulomb interaction between the valence-band electrons and the core electrons U(c). The spectra are influenced by the screening of the core hole in the initial state for Auger electron spectroscopy (AES), the sudden response of the valence-band electrons after the destruction of the core hole and, for appearance-potential spectroscopy (APS), by the scattering at the core hole in the final state. These effects become important especially for systems with partially filled energy bands. For APS, however, the U(c) interaction already yields nontrivial effects for the limiting case of a completely empty valence band. The localized core hole implies a breakdown of translational symmetry in the distribution of the valence-band electrons, which renders the calculation more difficult. But, extending the theory to finite temperatures, we will show that the translational symmetry may be reestablished in a formal way. Both the AES and APS intensities are directly related to a proper three-particle spectral density that exactly reflects the crystal periodicity. Within the framework of the single-band Hubbard model, which is extended to include the U(c) interaction, we calculate the three-particle spectral density in a generalized ladder approximation. The U(c) interaction is treated by means of perturbation theory. We develop the theory for the zeroth- and first-order contributions and look at the interesting limiting cases of a completely filled and empty valence band.