On the Origin of the 2DEG Carrier Density at the LaAlO$_3$/SrTiO$_3$ Interface

TL;DR

This study investigates the discrepancy between expected and observed carrier densities at the LaAlO$_3$/SrTiO$_3$ interface by using density-functional calculations to analyze electron subbands and their transport contributions.

Contribution

The paper provides a detailed density-functional analysis revealing multiple electron subbands and their roles, explaining the lower-than-expected carrier density at the interface.

Findings

Electrons occupy multiple subbands at the interface.

Some electrons are localized within a single layer.

Others are extended and contribute to transport.

Abstract

Transport measurements of the two-dimensional electron gas (2DEG) at the LaAlO$_3$/SrTiO$_3$ interface have found a density of carriers much lower than expected from the "polar catastrophe" arguments. From a detail density-functional study, we suggest how this discrepancy may be reconciled. We find that electrons occupy multiple subbands at the interface leading to a rich array of transport properties. Some electrons are confined to a single interfacial layer and susceptible to localization, while others with small masses and extended over several layers are expected to contribute to transport.