Orbital ordering under reduced symmetry in transition metal perovskites: Oxygen vacancy in SrTiO3

By using a combination of density function theory and model Hamiltonian analysis, we explain the general electronic structure features induced by an oxygen vacancy (OV) in SrTiO3. We show that the most important effect caused by an oxygen vacancy is the direct on-site coupling between the 3d(3z)2(-r)2 and 4s,4p orbitals of Ti atoms adjacent to the vacancy caused by lifting of the local cubic symmetry. This would be the case for any transition metal perovskite under symmetry-reduced environments such as an interface, surface, or a defect. We find that the OV-induced localized state is highly one dimensional and is mainly composed of Ti 3(d3)z2(-r)2 orbitals along the Ti-OV-Ti axis (defined as the z axis) and Ti 4s,4p orbitals at the OV site. The oxygen vacancy does not lead to Ti t(2g)-based localized states.