Oxygen vacancy roles in transition metal oxides and related heterostructures

Transition metal oxides have exhibited many emergent phenomena. Recent advancements in growth techniques have made their applications in devices even more promising. During growth, an oxygen vacancy is one of the most abundant types of point defects. In this dissertation, I use density functional theory to investigate the oxygen vacancy role in transition metal oxides and related heterostructures. I show how oxygen vacancies influence the phonon spectrum of HfO₂ films. With ab-initio calculations, a spin-polarized two-dimensional electron gas is predicted at the interface of a ferromagnetic insulator EuO and oxygen-deficient SrTiO₃. Experimental results agree with the theoretical discovery and a positive linear magnetoresistance is observed for this two-dimension electron system. Based on the first principles calculation results, we use the conventional Boltzmann transport theory to show that Zeeman splitting caused by proximity magnetism from EuO is responsible for the behavior of this unusual magnetoresistance.