Electron-Electron Interaction Effects on the Appearance Potential Spectroscopy of Metals.

Effects of electron-electron interactions on the appearance potential spectroscopy (APS) of simple metals have been calculated using many-body perturbation techniques. These effects include plasmon satellites, modification of the main band due to single particle excitations, and the anomalous edge behavior. The formalism uses an electron gas model, with electron-electron interaction effects calculated using the Random Phase Approximation (RPA) to describe polarization of the gas. The first plasmon satellite and single-particle excitation spectra are calculated using an S- and T-matrix approach. Plasmon dispersion is considered along with electron recoil. The edge structure is handled by an extension of the Nozieres-DeDominicis approach to include regions away from the threshold, which allows the use of a non -separable (realistic) scattering potential. Numerical calculations have been carried out for the 1s and 2p APS spectra of aluminum. The plasmon structures calculated exhibit features which depend on the extent of plasmon dispersion in the metal. The single particle spectrum is smooth except near the threshold. A power law behavior is found near the APS threshold, consistent with other edge theories and with experiment.