Evidence for correlation effects inSr2RuO4from resonant and x-ray photoemission spectroscopy

We study the electronic structure of ${\mathrm{Sr}}_2$ ${\mathrm{RuO}}_4$, a noncuprate layered superconductor (${\mathit{T}}_{\mathit{c}}$=0.93 K), using electron spectroscopy. X-ray photoemission spectroscopy shows that the single particle occupied density of states (DOS) is in fair agreement with the calculated DOS. However, resonant photoemission spectroscopy across the Ru 4p-4d threshold establishes the existence of a correlation satellite to the Ru 4d band. The results indicate substantial charge-transfer character at the Fermi level, with on-site correlations ${\mathit{U}}_{\mathit{dd}}$ comparable in magnitude to the Ru-O hopping integral, like the cuprates. © 1996 The American Physical Society.