First-principle study of metal oxide thin films: Electronic and magnetic properties of confined d electrons

Abstract

Abstract In bulk transition metal oxides, d electrons exhibit intriguing electronic and magnetic properties. Thanks to recent progress of epitaxial growth techniques, metal oxide thin films and interfaces can now be synthesized and controlled at atomic scales so that valence d electrons are confined within a region of a few unit cells (~ 1 nm) in the direction of the epitaxial growth. As a result of the confinement, many novel physical phenomena occur including orbital-selective quantum well states, metal-insulator transitions, superconductivity tunable by gate voltage, enhanced thermoelectric effects, thickness dependent ferromagnetism, strong spin-orbit coupling effects, and tunable correlation strength; all of which result in rich-phase diagrams including partially exotic ground states involving spin, charge, and orbital degrees of freedom. In this chapter, we review the recent first-principle studies of electronic and magnetic properties of confined d electrons in metal oxide thin films. The review includes a wide range of first-principle (parameter-free) studies, including density functional theory (DFT), ab inito-based tight binding (via Wannier projection) method, as well as their combination with quantum many-body techniques like dynamical mean field theory (DMFT). We focus on single particle-level physics as well as effects from spin-orbit coupling and strong electronic correlation. We discuss in detail how the physics can be controlled by the “knobs” unique to the thin-film system such as the crystalline orientation, dimensionality, and epitaxial strain.