Prediction of spin-polarized two-dimensional t2g electron gas at oxygen-deficient SrTiO3/EuO interface*

By performing first-principles calculations, we predict the existence of a spin-polarized two-dimensional electron gas (2DEG) at the interface of a ferromagnetic insulator EuO and oxygen-deficient SrTiO₃ (STO). The carriers are generated by the oxygen vacancies in STO near the interface and have predominantly Ti-t_2g orbital character. At the interface, the split off d_xy-derived conduction band of STO is fully spin-polarized as is the in-gap vacancy-related deep state, found below the conduction band edge. The electron in the gap state is aligned ferromagnetically with EuO. Combined with the calculated electronic structure, we use the conventional 2D Boltzmann transport theory to explain the observed positive linear magnetoresistance (LMR) in this system. We attribute the LMR to the proximity-induced-Zeeman effect. We develop a three-orbital model to explain how the DFT result depends on the strength of the on-site Coulomb repulsion U. The calculations suggest a possible mechanism for generating spin-polarized 2DEG for future spintronic applications.