  The physics of oxide superlattices is considered for pristine (001)
multilayers of the band insulators LaAlO3 and SrTiO3 with alternating p and n
interfaces. First principles results and a model of capacitor plates offer a
simple paradigm to understand their dielectric properties and the insulator to
metal transition (IMT) at interfaces with increasing layer thickness. The
charge at insulating interfaces is 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.
