 |
Center for Nonlinear Studies |
It is now routine to create two-dimensional conductors by growing complex oxide heterostructures. Like covalent semiconductor quantum wells, these oxide two-dimensional electron systems make it possible to achieve large relative changes in electron density by electrostatic gating. At the same time they exhibit stronger interaction effects and often exhibit complex phenomena traditionally associated with three-dimensional oxides, e.g. magnetism and superconductivity in close proximity, metal-insulator phase transitions, and electronic phase separation. In my talk I will address the case of two-dimensional d-orbital bands with far fewer than one conduction electron per unit cell, emphasizing the importance of Coulomb interactions far from the Mott-Hubbard regime. I will begin by introducing a generic model that captures the important influence of anisotropic and orbital-dependent hopping. We have used this model to understand quasiparticle properties within the GW approximation, which predicts that Coulomb interactions result in a large effective-mass enhancement and an accompanying reduction in Fermi-surface-shape anisotropy. I’ll conclude by discussing a new variational theory for multi-band two-dimensional electron gases that captures the interplay between the electrostatic confining potential at the interface, orbital-dependent electronic hopping, and electron-electron interactions. When applied to the oxide two-dimensional electron gas model a novel sequence of orbital and spin ordered ground states are predicted at experimentally realizable electron densities. I will discuss these results in the context of recent magneto-transport experiments.
Host: Nikolai Sinitsyn