Off-Site Contributions to Electron Correlation; An Extension to the Hubbard Model Studied by Auger Spectroscopy

A new theory of the lineshape of CVV Auger processes has been developed which extends the Hubbard Hamiltonian to include off-site correlation effects. The new theory shows that the neglect of off-site correlations explains the failure of the standard Cini-Sawatzky model of CVV processes to yield simultaneous agreement with the experimental kinetic energy and profile of the N6,7O4,5O4,5 Auger spectra of Au which correspond to the U > W, quasi-atomic, case. The theory predicts that the contribution from off-site correlations will be less important in the U < W, bandlike region, and this is shown to be consistent with the results of high-resolution measurements of the KVV spectrum of Si.