Two-dimensional electron systems in perovskite oxide heterostructures: Role of the polarity-induced substitutional defects

TL;DR

This study investigates the microscopic origins of the two-dimensional electron system at LaAlO3/SrTiO3 interfaces, revealing distinct distributions of interface carriers and their roles in conductivity and magnetism.

Contribution

It provides a detailed spectroscopic analysis showing the spatial distribution of Ti 3d carriers and polarity-induced defects, clarifying their roles in interfacial phenomena.

Findings

Ti 3d carriers are within 3 unit cells of the SrTiO3 interface.

Polarity-induced Ti-on-Al antisite defects are in the first 3 unit cells of LaAlO3.

Different interface carriers are responsible for conductivity and magnetism.

Abstract

The discovery of a two-dimensional electron system (2DES) at the interfaces of perovskite oxides such as LaAlO3 and SrTiO3 has motivated enormous efforts in engineering interfacial functionalities with this type of oxide heterostructures. However, its fundamental origins are still not understood, e.g. the microscopic mechanisms of coexisting interface conductivity and magnetism. Here we report a comprehensive spectroscopic investigation of the depth profile of 2DES-relevant Ti 3d interface carriers using depth- and element-specific techniques, standing-wave excited photoemission and resonant inelastic scattering. We found that one type of Ti 3d interface carriers, which give rise to the 2DES are located within 3 unit cells from the n-type interface in the SrTiO3 layer. Unexpectedly, another type of interface carriers, which are polarity-induced Ti-on-Al antisite defects, reside in the first 3 unit cells of the opposing LaAlO3 layer (~10 {\AA}). Our findings provide a microscopic picture of how the localized and mobile Ti 3d interface carriers distribute across the interface and suggest that the 2DES and 2D magnetism at the LaAlO3/SrTiO3 interface have disparate explanations as originating from different types of interface carriers.