Strain and spin-orbit coupling induced orbital ordering in the Mott insulatorBaCrO3

Abstract

Using ab initio calculations, we have investigated an insulating tetragonally distorted perovskite ${\mathrm{BaCrO}}_{3}$ with a formal $3{d}^{2}$ configuration, the volume of which is apparently substantially enhanced by a strain due to ${\mathrm{SrTiO}}_{3}$ substrate. Inclusion of both correlation and spin-orbit coupling (SOC) effects leads to a metal-insulator transition and in-plane zigzag orbital ordering (OO) of alternating singly filled ${d}_{xz}+i{d}_{yz}$ and ${d}_{xz}\ensuremath{-}i{d}_{yz}$ orbitals, which results in a large orbital moment ${M}_{L}\ensuremath{\approx}\ensuremath{-}0.78{\ensuremath{\mu}}_{B}$ antialigned to the spin moment ${M}_{S}\ensuremath{\approx}2|{M}_{L}|$ in Cr ions. Remarkably, this ordering also induces a considerable ${M}_{L}$ for apical oxygens. Our findings show metal-insulator and OO transitions, driven by an interplay among strain, correlation, and SOC, which is uncommon in $3d$ systems.