Phase separation from electron confinement at oxide interfaces

TL;DR

This paper demonstrates that electron confinement at oxide interfaces can intrinsically cause phase separation, explaining the observed inhomogeneity through a self-consistent electrostatic potential calculation.

Contribution

It introduces a self-consistent electrostatic model showing phase separation as an intrinsic mechanism at oxide interfaces.

Findings

Electron confinement can induce phase separation.

The mechanism explains interface inhomogeneity.

Negative compressibility leads to phase separation.

Abstract

Oxide heterostructures are of great interest both for fundamental and applicative reasons. In particular the two-dimensional electron gas at the LaAlO$_3$/SrTiO$_3$ or LaTiO$_3$/SrTiO$_3$ interfaces displays many different physical properties and functionalities. However there are clear indications that the interface electronic state is strongly inhomogeneous and therefore it is crucially relevant to investigate possible intrinsic electronic mechanisms underlying this inhomogeneity. Here the electrostatic potential confining the electron gas at the interface is calculated self-consistently, finding that the electron confinement at the interface may induce phase separation, to avoid a thermodynamically unstable state with a negative compressibility. This provides a generic robust and intrinsic mechanism for the experimentally observed inhomogeneous character of these interfaces.