Electronic structure of SrRuO₃

Full text: The electronic structure of the SrRuO₃ ruthenate was studied using several spectroscopic techniques. The Ru 4p core-level and valence band were probed with high energy photoemission spectroscopy (PES), and the conduction band with x-ray absorption spectroscopy (XAS). The experimental results were interpreted with an extended cluster model, which was solved using the configuration interaction method. The theoretical results are in good agreement with the experiments, and were able to reproduce all the spectra with the same set of parameters. The calculations yielded a metallic and ferromagnetic ground state dominated by the 4d 5L configuration, showing that the compound is in the negative charge transfer regime. The core-level spectrum presents structures at low and high binding energies related to well- and poorly-screened states, respectively. In the valence band spectrum, the Ru 4d region, near the Fermi level, shows the coherent and incoherent features, associated with the well-screened 4d 5LC and 4d 5L 2 states. On the other hand, the O 2p region, at higher energies, presents some ruthenium contribution associated with the poorly-screened 4d 3 and 4d 4L states. This shows that the screening mechanisms in the core-level and valence band regions are similar, as previously suggested. We were also able to extract the Ru 4d contribution for the valence band spectrum by performing Ru L3 resonant photoemission spectroscopy (RPES). The O1s x-ray absorption spectrum showed the O 2p contribution to the conduction band. The structures in this spectrum are attributed to the unoccupied parts of the t2g and eg sub-bands. The effects in this region are governed by the relatively large crystal field splitting (10 Dq) and intratomic exchange interaction (J). Therefore, the electronic structure of SrRuO₃ is dominated by a strong Ru 4d - O 2p covalent character, and the oxygen states play an important role in the physical properties of this system. (author)