Using RIXS to uncover elementary charge and spin excitations in correlated materials

TL;DR

This paper uses advanced numerical methods to analyze RIXS experiments on cuprates, revealing how polarization and geometry influence the spectral features and their relation to charge and spin excitations.

Contribution

It provides a detailed theoretical understanding of RIXS cross-sections in cuprates, emphasizing the role of polarization and the limitations of simplified models.

Findings

RIXS spectral shape in cross-polarized channel resembles spin structure factor.

Polarization significantly affects RIXS spectral features.

Simplified models cannot capture all RIXS spectral complexities.

Abstract

Despite significant progress in resonant inelastic x-ray scattering (RIXS) experiments on cuprates at the Cu L-edge, a theoretical understanding of the cross-section remains incomplete in terms of elementary excitations and the connection to both charge and spin structure factors. Here we use state-of-the-art, unbiased numerical calculations to study the low energy excitations probed by RIXS in undoped and doped Hubbard model relevant to the cuprates. The results highlight the importance of scattering geometry, in particular both the incident and scattered x-ray photon polarization, and demonstrate that on a qualitative level the RIXS spectral shape in the cross-polarized channel approximates that of the spin dynamical structure factor. However, in the parallel-polarized channel the complexity of the RIXS process beyond a simple two-particle response complicates the analysis, and demonstrates that approximations and expansions which attempt to relate RIXS to less complex correlation functions can not reproduce the full diversity of RIXS spectral features.