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.