Collective mode excitations and simulated $L$-edge resonant-inelastic x-ray scattering spectra in antiferromagnetic Ca$_2$RuO$_4$

TL;DR

This study models and simulates the low-energy magnetic excitations in Ca$_2$RuO$_4$, demonstrating how RIXS spectra can reveal detailed information about transverse modes and their polarization dependence.

Contribution

It introduces a theoretical framework combining the Hubbard model, RPA, and RIXS simulations to analyze magnetic excitations in Ca$_2$RuO$_4$, aligning well with experimental data.

Findings

Transverse mode dispersion matches neutron scattering data.

RIXS spectra clearly show transverse mode dispersion.

Polarization dependence distinguishes in-plane and out-of-plane excitations.

Abstract

Using the three-orbital Hubbard model, we investigate the low-energy excitation spectra in the antiferromagnetic phase of Ca$_2$RuO$_4$. We calculate the dynamical susceptibilities in the low-energy region by the random phase approximation and find that the anisotropic dispersion of the transverse mode is in good agreement with the spectra recently reported by inelastic neutron scattering experiments. By the fast-collision approximation, we simulate the resonant inelastic x-ray scattering (RIXS) spectra of the Ru $L_3$ edge from the dynamical susceptibilities. We show that the dispersion of the transverse mode is clearly observed in the calculated RIXS spectra and that the polarization dependence of the incident x rays enables one to distinguish between the excitations of the in-plane transverse mode and out-of-plane transverse mode.