Interface relaxation and electrostatic charge depletion in the oxide heterostructure LaAlO3/SrTiO3

TL;DR

This study uses density functional theory to analyze how structural relaxation and electrostatic effects influence the electronic properties of LaAlO3/SrTiO3 heterostructures, revealing thickness-dependent transitions between metallic and insulating states.

Contribution

It provides a detailed theoretical analysis of the interplay between lattice distortions and electrostatic effects in oxide heterostructures, highlighting the impact of film thickness on electronic phases.

Findings

Elongation of TiO6 octahedra enhances metallicity.

Reduction of film thickness leads to charge depletion and insulating behavior.

Inversion of TiO6 distortion pattern occurs for films thinner than four LaAlO3 layers.

Abstract

Performing an analysis within density functional theory, we develop insight into the structural and electronic properties of the oxide heterostructure LaAlO3/SrTiO3. Electrostatic surface effects are decomposed from the internal lattice distortion in order to clarify their interplay. We first study the interface relaxation by a multi-layer system without surface, and the surface effects, separately, by a substrate-film system. While elongation of the TiO6 octahedra at the interface enhances the metallicity, reduction of the film thickness has the opposite effect due to a growing charge depletion. The interplay of these two effects, as reflected by the full lattice relaxation in the substrate-film system, however, strongly depends on the film thickness. An inversion of the TiO6 distortion pattern for films thinner than four LaAlO3 layers results in an insulating state.