Core level and valence band spectroscopy of SrRuO₃: Electron correlation and covalence effects

We studied the electronic structure of SrRuO₃ using several spectroscopic techniques. These include (resonant) photoemission, x-ray absorption, and optical conductivity. The experimental results were interpreted using an extended cluster model, which takes into account electron correlation and the Ru 4d-O 2p covalence. The analysis shows that this material is in the negative charge transfer regime, where the ground state is dominated by the 4d5LI2; configuration with an occupation of 47%. This is mainly due to the relatively large crystal field and exchange splitting in the Ru 4d states. The electronic structure of SrRuO₃ is strongly influenced by the Ru 4d-O 2p hybridization. Thus, the oxygen states should be explicitly considered in the analysis of the physical properties of this system. However, correlation effects are also important in this system giving rise to the coherent peak in the valence band spectra.