Tuning the insulator-metal transition in oxide interfaces: An ab initio study exploring the role of oxygen vacancies and cation interdiffusion

Abstract

We investigate the structural, electronic, and magnetic properties of a particular interface in the oxide heterostructures LaAlO/SrTiO (LAO/STO) and TiO-anatase/LaAlO (TiO/LAO), namely the interface of AlO facing TiO, which is the energetically preferred one in the presence of interfacial oxygen vacancies. The optimum stacking for the ground state is different for each heterostructure with the interfacial Ti atoms being located either at hollow or bridge sites facing the AlO surface layer. This structural property determines the electronic character of the interface and as a consequence, in LAO/STO it is metallic while in TiO/LAO it can be semiconducting and magnetic for a large concentration of vacancies. In addition, we find that cation interdiffusion at this interface is an energetically favored defect in both heterostructures with interfacial vacancies. Its main effect is to increase the size of the band gap in the semiconducting case and to open up a gap in the metallic one, thus allowing for a tuning of a metal to insulator transition.