Distinct spin and orbital dynamics in Sr 2 RuO 4

The unconventional superconductor Sr 2 RuO 4 has long served as a benchmark for theories of correlated-electron materials. The determination of the superconducting pairing mechanism requires detailed experimental information on collective bosonic excitations as potential mediators of Cooper pairing. We have used Ru L 3 -edge resonant inelastic x-ray scattering to obtain comprehensive maps of the electronic excitations of Sr 2 RuO 4 over the entire Brillouin zone. We observe multiple branches of dispersive spin and orbital excitations associated with distinctly different energy scales. The spin and orbital dynamical response functions calculated within the dynamical mean-field theory are in excellent agreement with the experimental data. Our results highlight the Hund metal nature of Sr 2 RuO 4 and provide key information for the understanding of its unconventional superconductivity.