Resonant inelastic x-ray scattering study of Ca3Ru2O7

Abstract

We present a combined oxygen K-edge x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) study of the bilayer ruthenate Ca 3 Ru 2 O 7. Our RIXS experiments on Ca 3 Ru 2 O 7 were carried out on the overlapping planar and interplanar oxygen resonances, which are distinguishable from the apical one. Comparison to equivalent oxygen K-edge spectra recorded on band-Mott insulating Ca 2 RuO 4 is made. In contrast to Ca 2 RuO 4 spectra, which contain excitations linked to Mott physics, Ca 3 Ru 2 O 7 spectra feature only intra-t 2g ones that do not directly involve the Coulomb energy scale. As found in Ca 2 RuO 4 , we resolve two intra-t 2g excitations in Ca 3 Ru 2 O 7. Moreover, the lowest lying excitation in Ca 3 Ru 2 O 7 shows a significant dispersion, revealing a collective character different from what is observed in Ca 2 RuO 4. Theoretical modeling supports the interpretation of this lowest energy excitation in Ca 3 Ru 2 O 7 as a magnetic transverse mode with multiparticle character, whereas the corresponding excitation in Ca 2 RuO 4 is assigned to combined longitudinal and transverse spin modes. These fundamental differences are discussed in terms of the inequivalent magnetic ground-state manifestations in Ca 2 RuO 4 and Ca 3 Ru 2 O 7 .

Coherent propagation of spin-orbit excitons in a correlated metal

“…Extending our findings beyond Sr 2 RhO 4 , our insights into the differences of the SOE propagation in antiferromagnetic insulating versus metallic systems hold significant implications for a variety of 4d and 5d transition metal compounds, including those based on ruthenium 8,[66][67][68][69][70][71][72] . In particular, the charge fluctuation mechanism might also be critical for the SOE propagation in the correlated metal and superconductor Sr 2 RuO 4 , where previous RIXS experiments at the O K-edge have reported a spin-orbit entangled mode with an energy of a few hundred meV 67 and a study at the Ru L 3 -edge has identified dispersive branches of spin-orbital excitations 73 .…”