The interplay of electronic reconstructions, lattice distortions, and surface oxygen vacancies in insulator-metal transition of LaAlO$_{3}$/SrTiO$_{3}$

TL;DR

This study uses density functional theory to elucidate how electronic reconstructions, lattice distortions, and surface oxygen vacancies collectively drive the insulator-metal transition at LaAlO₃/SrTiO₃ interfaces, aligning with experimental observations.

Contribution

It provides a comprehensive model explaining the interplay of various factors causing the insulator-metal transition in LaAlO₃/SrTiO₃, including the role of surface oxygen vacancies.

Findings

Lattice distortions and charge redistribution dominate in the insulating state.

Surface oxygen vacancies induce conductivity and a discontinuous transition.

The model explains properties under different growth conditions.

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.