Spin-state transition and phase separation in a multiorbital Hubbard model

We study the spin-state transition and the phase separation involved in this transition based on the multiorbital Hubbard model. Multiple spin states are realized by changing the energy separation between two orbitals and the on-site Hund coupling. By utilizing the variational Monte-Carlo simulation, we analyze the electronic and magnetic structures in hole doped and undoped states. Electronic phase separation occurs between the low-spin band insulating state and the high-spin ferromagnetic metallic state. The difference in the band widths of the two orbitals is of prime importance for the spin-state transition and the phase separation.