Damping of spinful excitons in LaCoO3 by thermal fluctuations: Theory and experiment

We present Co L-3-edge resonant inelastic x-ray scattering (RIXS) of bulk LaCoO3 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 by using dynamical mean-field theory for hard-core bosons. Our results provide a detailed mechanism of how high-spin and IS excitations interact to establish the physical properties of cobaltite perovskites.