The electronic structure of <i>n</i>-doped ABO₃ perovskite metals from quantum Monte Carlo.

Some perovskites (PVs) are known to undergo metal-to-insulator transitions (MITs) when n-doped. In particular, the PV ferromagnet strontium cobaltite (SrCoO₃), undergoes an MIT when a critical level of ordered oxygen vacancies are present in the system. Concomitant topotactic and magnetic transitions can also occur, e.g., the oxygen-deficient SrCoO_2.5 phase is an anti-ferromagnet with a brownmillerite crystal structure. The cause of this nonintuitive MIT in these oxygen-deficient systems is not well understood. Density functional theory (DFT) calculations suggest that charge disproprtionation is often associated with the transition, but these systems have strong correlations that are beyond DFT. Furthermore, counting formal oxidation states in the oxygen-rich systems hints at the presence of ligand holes which would conceivably lead to passivation after n-doping. Here, we hypothesize that these systems are indeed self-hole doped and use diffusion Monte Carlo methods that include electron correlations exactly to gain clarity on the electronic/magnetic/structural transitions.