Disproportionation and Metallization at Low-Spin to High-Spin Transition   in Multiorbital Mott Systems
  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. 
Jan Kunes and Vlastimil Krapek
cond-mat.str-el cond-mat.mtrl-sci