Correlation effects in valence-band spectra of nickel silicides

We discuss the role of the electronic correlation in determining the line shapes of valence-band photoemission and Auger spectra of Ni silicides. Theoretical one-particle spectra, with correlation effects included by a perturbation approach to a degenerated Hubbard Hamiltonian, are compared with experimental energy-distribution curves. It is shown that for these compounds the electronic correlation is of crucial importance for describing valence-band photoemission. We also present the experimental line shapes of Ni $L_3\mathrm{VV}$ transitions and compare them with theoretical two-hole spectral densities. It is concluded that a band-theoretical approach can account for some important features of the experimental Auger spectra, but multiplet effects should be included for a more detailed description.