Switchable conductivity at the ferroelectric interface: Nonpolar oxides

We investigate theoretically the interface between a ferroelectric BaTiO3 film and a nonpolar insulating SrTiO3 substrate. We find that thin BaTiO3 (under 5 nm) can stabilize a nonpolarized state, and an additional metastable polarized state. While the nonpolarized state is insulating, for the polarized heterostructure, we discover the existence of two-dimensional charge carrier gases. In this case, the heterostructure undergoes an electronic reconstruction in order to prevent the polar catastrophe. The two-dimensional gases, formed as a result, screen the polarization, leading to a substantially reduced potential drop across the ferroelectric film. We emphasize that the two-dimensional electron and hole gases are created by the polarization of the sample, and are not due to the polar nature of the material or to doping.