Electronic structure ofSr2RuO4: X-ray fluorescence emission study

The results of measurements of O $1s$ total x-ray-fluorescence yield and Ru $N_{2,3}$ and O $K_{\alpha }$ x-ray fluorescence emission spectra of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and ${\mathrm{Sr}}_2{\mathrm{RuO}}_{4.25}$ are presented. An excitation energy dependence of the O $K_{\alpha }$ x-ray emission spectra (XES) was observed in both compounds. The energy dependence of the spectra is attributed to the excitation of inequivalent O (1) in-plane and O(2) apical oxygens. The O(1) $2p$ and O(2) $2p$ density of states distribution in the valence band of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ was found to be different in accordance with the results of band-structure calculations. O(1) $2p$ states are found to be mixed with Ru ${4d(t}_{2g})$ states providing the formation of $\pi$ bonds. While the O $K_a$ XES spectra are in fair agreement with band structure calculations, the theoretical two-peak distribution of Ru $N_{2,3}$ XES is found to be different with respect to the intensity ratios and widths of the peaks of Ru $N_{2,3}$ XES. These differences are attributed to a decrease of intensity of radiative $4\overrightarrow{d}4p$ transitions in the vicinity of the Fermi level (where the localization of Ru $4d$ states is higher than at the bottom of the valence band) due to a strong Koster-Kronig transition.