Distinct spin and orbital dynamics in Sr$_{2}$RuO$_{4}$

TL;DR

This study uses resonant inelastic x-ray scattering to map electronic excitations in Sr$_2$RuO$_4$, revealing distinct spin and orbital dynamics crucial for understanding its unconventional superconductivity.

Contribution

It provides the first comprehensive experimental mapping of spin and orbital excitations across the Brillouin zone in Sr$_2$RuO$_4$, aligning with dynamical mean-field theory calculations.

Findings

Identification of multiple dispersive spin and orbital excitation branches.

Excellent agreement between experimental data and theoretical calculations.

Confirmation of Hund metal behavior in Sr$_2$RuO$_4$.

Abstract

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.