The interplay of electronic reconstructions, lattice distortions, and surface oxygen vacancies in insulator-metal transition of LaAlO${}_3$/SrTiO${}_3$

Abstract

The mechanism responsible for the extraordinary interface conductivity of LaAlO${}_3$ on SrTiO${}_3$ and its insulator-metal transition remains controversial. Here, using density functional theory calculations, we establish a comprehensive and coherent picture that the interplay of electronic reconstructions, lattice distortions, and surface oxygen vacancies fully compensates the polarization potential divergence in LaAlO${}_3$/SrTiO${}_3$, explaining naturally the experimental observations under different conditions. While lattice distortions and a charge redistribution between LaO and AlO${}_2$ sub-layers play a dominant role in insulating state, a spontaneous appearance of 1/4 oxygen vacancies per AlO${}_2$ sub-layer at the LaAlO${}_3$ surface accompanied by 0.5$e^{-}$ charge-transfer into the interface is responsible for interface conductivity and the discontinuous transition in LaAlO${}_3$/SrTiO${}_3$. Our model also explain properties of LaAlO${}_3$/SrTiO${}_3$ prepared with different growth conditions.

Physical Review B (accepted)