Resonant Inelastic X-ray Scattering Study of Ca3Ru2O7
Abstract
We present a combined oxygen K-edge x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) study of the bilayer ruthenate Ca3Ru2O7. Our RIXS experiments on Ca3Ru2O7 were carried out on the overlapping planar and inter-planar oxygen resonances, which are distinguishable from the apical one. Comparison to equivalent oxygen K-edge spectra recorded on band-Mott insulating Ca2RuO4 is made. In contrast to Ca2RuO4 spectra, which contain excitations linked to Mott physics, Ca3Ru2O7 spectra feature only intra-t2g ones that do not directly involve the Coulomb energy scale. As found in Ca2RuO4, we resolve two intra-t2g excitations in Ca3Ru2O7. Moreover, the lowest lying excitation in Ca3Ru2O7 shows a significant dispersion, revealing a collective character differently from what is observed in Ca2RuO4. Theoretical modelling supports the interpretation of this lowest energy excitation in Ca3Ru2O7 as a magnetic transverse mode with multi-particle character, whereas the corresponding excitation in Ca2RuO4 is assigned to combined longitudinal and transverse spin modes. These fundamental differences are discussed in terms of the inequivalent magnetic ground-state manifestations in Ca2RuO4 and Ca3Ru2O7.