Switchable two-dimensional electron gas at the interface of a ferroelectric and nonpolar insulator: BaTiO3/SrTiO3

We theoretically investigate the interface between a ferroelectric BaTiO3 film and a nonpolar insulating SrTiO3 substrate. We find that thin BaTiO3, under 5 nm, can stabilize two polarization states. While the nonpolarized state is insulating, for the polarized heterostructure, we discovered the existence of two-dimensional 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 is not due to the polar nature of either material or doping.