Nature of the electronic states in the layered perovskite noncuprate superconductorSr2RuO4

Near-edge x-ray-absorption and photoemission spectra of the noncuprate superconductor ${\mathrm{Sr}}_2$Ru${\mathrm{O}}_4$ are presented. Holes close to the Fermi level are determined by Ru $4d_{\mathrm{xy}}$, $4d_{\mathrm{xz}}$, and $4d_{\mathrm{yz}}$ antibonding states. The density of the occupied states at the Fermi level derived from photoemission is higher than in the cuprates and these states have predominantly Ru $4d$ character. Angle-resolved photoemission yields a width of the occupied part of the conduction bands that is reduced by a factor of 2 in comparison to band-structure calculations. The importance of electron correlations is also evident in the appearance of screened final states in the Ru $3d$ core-level spectrum.