Oxide superlattices with alternating p and n interfaces

The physics of oxide superlattices is considered for pristine (001) multilayers of the band insulators LaAlO(3) and SrTiO(3) with alternating p and n interfaces. A model of charged capacitor plates offers a simple paradigm to understand their dielectric properties and the insulator to metal transition (IMT) at interfaces with increasing layer thicknesses. The model is supported by first-principles results based on density-functional theory. The charge at insulating interfaces is argued and found to be as predicted from the formal ionic charges, not populations. Different relative layer thicknesses produce a spontaneous polarization of the system, and allow manipulation of the interfacial electron gas. Large piezoresistance effects can be obtained from the sensitivity of the IMT to lateral strain. Carrier densities are found to be ideal for exciton condensation.