Doping and interfaces in complex oxide heterostructures and superlattices from first principles

Charge transfer between unit-cell-scale layers of different materials in superlattices and heterostructures can produce modulation doping with high carrier concentrations. In complex oxides, changes in carrier concentration can lead to dramatic changes in the structure and properties, including transitions to distinct phases. The degree of the charge transfer, the character of the electronic states occupied by the transferred charge, and the resulting changes in structure, phonons, transport and optical properties can be readily determined from first principles calculations. In this talk, I will discuss recent results on a range of systems, including materials design of high mobility ferroelectrics for ferroelectric field effect transistors, modulation doping and quantum confinement in BaSnO₃ layers in superlattices, charge-order-driven ferroelectricity in transition-metal perovskite superlattices, and new doping-induced phases in nickelates and nickelate/iridate superlattices, in which the added carriers localize on the Ni and Ir ions to produce novel charge, orbital and spin ordering.