The electronic and optical properties of low dimensional metal-oxide heterostructures

Functional metal-oxide materials exhibit many intriguing phenomena and attract the intensive research in condensed matter physics as well as materials science. Furthermore, the metal-oxide-based heterostructures demonstrate unusual low-dimensional effects due the symmetry breaking at the interface. I have studied several low dimensional heterostructures from the theoretical and computational perspectives. I have developed a multiscale simulation framework, based on density functional theory that covers the microscopic (~ 10⁻⁹ m), mesoscopic (~ 10⁻⁸ m) and macroscopic (~ 10⁻⁷ m) length scale. The first heterointerface I discuss is Si/EuO. Using density functional theory, I demonstrate how the interfacial oxidation influences the band alignment between the Si substrate and EuO, which is essential for the EuO applications in spintronic devices. The second system is the two-dimension electron gas at the oxygen deficient SrTiO₃/EuO interface in the BaTiO₃/SrTiO₃/EuO heterostructure. I demonstrate that the spontaneous polarization in BaTiO₃ can influence the intrinsic electric field across SrTiO₃/EuO and control the location of the two-dimensional electron gas in either SrTiO₃ side or EuO side. The switchable functionality due to the presence of BaTiO₃ offers a promising way to control spin polarized carriers in spintronic devices. Next, I focus on the magnetoelectric effect at the BaTiO₃/Ni interface and demonstrate that compared to bulk multiferroic materials, artificially engineered interface structures have much larger magnetoelectric coupling coefficients due to the symmetry breaking at the interface. The fourth system I study is the BaSnO₃-based quantum well. By utilizing the intersubband transitions, the BaSnO₃-based quantum well structure has high nonlinear optical susceptibility as well as broad optical spectral range, from THz to near visible light region, which has promising applications as nonlinear light source in photonic integrated circuit. The fifth system discussed in this thesis is the epitaxial BaTiO₃ films deposited on different substrates. Compared with the bulk material, the behavior of thin films of BaTiO₃ is different due to the complicated boundary conditions. To describe a thin film, I use phase field simulations implemented with a finite element method. The simulations are able to reveal the complex domain morphology.