Structural relaxation and metal-insulator transition at the interface between SrTiO3 and LaAlO3

TL;DR

This study investigates how structural relaxation influences the electronic properties and metal-insulator transition at LaAlO3/SrTiO3 interfaces using LSDA+U calculations, highlighting the importance of interface structure and termination.

Contribution

It provides a detailed computational analysis of the effects of atomic relaxation and interface termination on electronic states and phase transitions at LaAlO3/SrTiO3 interfaces.

Findings

Structural relaxation induces polarization in SrTiO3 and Jahn-Teller splitting in sandwiches.

Relaxation in AlO2-terminated bilayers leads to an insulator-metal transition.

The interface structure and termination significantly affect electronic properties.

Abstract

The electronic structure of interfaces between LaAlO$_3$ and SrTiO$_3$ is studied using local spin density approximation (LSDA) with intra-atomic Coulomb repulsion (LSDA+U). We find that the nature of the interface metallic states is strongly affected by the type of the structure (sandwich or bilayer) and by the termination surface of LaAlO$_3$. In all structures the atomic relaxation plays a crucial role in the electronic properties of the system. While in sandwiches the structural relaxation produces a significant polarization in SrTiO$_3$ and Jahn-Teller like splitting of Ti $3d_{xy}$ orbitals, in AlO$_2$-terminated bilayers the relaxation occurs primarily in LaAlO$_3$ and results in an insulator-metal transition which has been observed experimentally with increasing thickness of the LaAlO$_3$ layer.