Correlation effects inSr2RuO4andCa2RuO4: Valence-band photoemission spectra and self-energy calculations

Abstract

We have studied the electronic structure of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ using x-ray photoemission spectroscopy (XPS) and subsequent model calculations. While the ${t}_{2g}$ band of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ has substantial spectral weight at the Fermi level, that of ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ has no spectral weight at ${E}_{F}$ and shows a peak at $\ensuremath{-}1.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. In the valence-band XPS spectrum of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, a satellite structure of the ${t}_{2g}$ band is observed. In order to explain the spectral features, we have carried out band-structure calculations using the unrestricted Hartree-Fock (HF) approximation and found good agreement with the experimental result for ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$. In order to explain the satellite structure of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, we have performed second-order perturbation calculations of the self-energy corrections around the unrestricted HF solution of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$.