Electronic structure trends in the Srn+1RunO3n+1 family (n=1,2,3)

The identification of electronic states and the analysis of their evolution with n is key to understanding n-layered ruthenates. To this end, we combine polarization-dependent O 1s x-ray absorption spectroscopy, high-purity Sr_n+1Ru_nO_3n+1 (n=1,2,3) single crystals, and ab initio and many-body calculations. We find that the energy splitting between the empty x²-y² and 3z²-1 state is considerably smaller than previously suggested and that, remarkably, Sr bands are essential to understanding the spectra. At low energy, we identify the main difference among the materials with a substantial rearrangement of t_2g orbital occupations with increasing n. This rearrangement is controlled by the interplay of Coulomb repulsion, dimensionality, and changes in the t_2g crystal field.