Disproportionation and Metallization at Low-Spin to High-Spin Transition in Multiorbital Mott Systems

TL;DR

This paper investigates the thermally driven spin state transition in a two-orbital Hubbard model, revealing a spin disproportionated phase with checkerboard order and its dependence on crystal field splitting, using dynamical mean-field theory.

Contribution

It introduces a minimal model for LaCoO3's spin transition and uncovers a spin disproportionated phase with checkerboard order via advanced computational methods.

Findings

Disproportionated phase exists at intermediate temperatures.

High-temperature transition involves vanishing charge gap.

Disproportionated phase disappears with increasing crystal-field splitting.

Abstract

We study the thermally driven spin state transition in a two-orbital Hubbard model with crystal field splitting, which provides a minimal description of the physics of LaCoO3. We employ the dynamical mean-field theory with quantum Monte-Carlo impurity solver. At intermediate temperatures we find a spin disproportionated phase characterized by checkerboard order of sites with small and large spin moments. The high temperature transition from the disproportionated to a homogeneous phase is accompanied by vanishing of the charge gap. With the increasing crystal-field splitting the temperature range of the disproportionated phase shrinks and eventually disappears completely.