Two-dimensional electron gas at the Ti-diffused BiFeO3/SrTiO3 interface

Oxide heterostructures with the broken translational symmetry often trigger a two-dimensional quantum confinement and associated unique electronic properties that cannot be observed in bulk constituents. Particular interest is devoted to the formation of two-dimensional electron gas (2DEG) at heterointerfaces between two insulators, which offers a fertile ground for fabricating advanced electronic devices. Here, we combine atomic force microscopy, transmission electron microscopy, and atomistic first-principles calculations to demonstrate that the (100) BiFeO3/SrTiO3 interface takes on a metallic nature and a 2DEG is generated at this interface. Our findings also reveal that the electronic reconstruction due to the polar discontinuity and the variation in valence state of Ti arising from diffusion of Ti cations in SrTiO3 to Fe sites of BiFeO3 are critical to the formation of 2DEG at the heterointerface.