Orbital-Resolved Soft X-ray Spectroscopy Measurnents of Sr$_{2}$RuO$_{4}$ Electronic Structure.

Strontium ruthenate (Sr$_{2}$RuO$_{4})$ is a spin-triplet superonductor$^{1}$ of the Ruddlesden-Popper (RP) series with n=1. We have studied the electronic structure of single crystals of this system by density functional theory (DFT) calculations and soft x-ray emission and absorption measurements at the oxygen K edge (530 eV) and find that DFT calculations provide an excellent model to characterize the molecular orbitals corresponding to the inequivalent O sites in this perovskite compound. The linearly polarized radiation excites primarily O[1] (planar) sites at almost normal incidence and O[2] (apical) sites at grazing incidence. Our results suggest a larger level of hybridization between the Ru d and the O p$_{ }$states in the RuO$_{2}$ planes than between the Ru and apical O atoms, which also implies more localized bonding along the apical direction than the planar direction. This work was supported by DOE grant No. DE-FG02-05ER-46183. 1)Y. Maeno, et al, Nature 372, 532 (1994).