Correlation effects in Sr₂RuO₄ and Ca ₂RuO₄: Valence-band photoemission spectra and self-energy calculations

We have studied the electronic structure of Sr₂RuO₄ and Ca₂RuO₄ using x-ray photoemission spectroscopy (XPS) and subsequent model calculations. While the t_2g band of Sr ₂RuO₄ has substantial spectral weight at the Fermi level, that of Ca₂RuO₄ has no spectral weight at E_F and shows a peak at -1.8 eV. In the valence-band XPS spectrum of Sr ₂RuO₄, 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 Ca ₂RuO₄. In order to explain the satellite structure of Sr₂RuO₄, we have performed second-order perturbation calculations of the self-energy corrections around the unrestricted HF solution of Sr₂RuO₄.