Damping of spinful excitons in LaCoO$_3$ by thermal fluctuations: Theory and experiment

TL;DR

This study combines high-resolution RIXS experiments and dynamical mean-field theory to investigate how thermal fluctuations damp spinful excitons in LaCoO$_3$, revealing their dispersion, damping, and interactions across the spin-state crossover.

Contribution

It provides a detailed theoretical and experimental analysis of spin exciton damping in LaCoO$_3$, introducing a model of mobile IS excitons with strong interactions.

Findings

Observation of dispersive IS excitations at low temperature

Damping and bandwidth reduction of IS excitations with increasing temperature

Agreement between experimental data and dynamical mean-field theory model

Abstract

We present Co $L_3$-edge resonant inelastic x-ray scattering (RIXS) of bulk LaCoO$_3$ across the thermally-induced spin-state crossover around 100~K. Owing to a high energy resolution of 25~meV, we observe unambiguously the dispersion of the intermediate-spin (IS) excitations in the low temperature regime. Approaching the intermediate temperature regime, the IS excitations are damped and the bandwidth is reduced. The observed behavior can be well described by a model of mobile IS excitons with strong attractive interaction, which we solve using dynamical mean-field theory for hard-core bosons. Our results provide a detailed mechanism of how high-spin (HS) and IS excitations interact to establish the physical properties of cobaltite perovskites.