Intrinsic origin of the two-dimensional electron gas at polar oxide interfaces

TL;DR

This paper demonstrates that the intrinsic polar catastrophe mechanism causes the formation of a two-dimensional electron gas at polar oxide interfaces, with conductivity emerging after a critical film thickness related to the built-in electric field.

Contribution

It provides conclusive evidence that the polar-catastrophe model explains the intrinsic origin of doping at polar oxide interfaces, supported by experimental scaling with film thickness and electric field.

Findings

Conductivity appears above a critical thickness proportional to the electric field.

The critical thickness scales with the strength of the built-in electric field.

Results confirm the polar-catastrophe model as the intrinsic doping mechanism.

Abstract

The predictions of the polar catastrophe scenario to explain the occurrence of a metallic interface in heterostructures of the solid solution(LaAlO$_3$)$_{x}$(SrTiO$_3$)$_{1-x}$ (LASTO:x) grown on (001) SrTiO$_3$ were investigated as a function of film thickness and $x$. The films are insulating for the thinnest layers, but above a critical thickness, $t_c$, the interface exhibits a constant finite conductivity which depends in a predictable manner on $x$. It is shown that $t_c$ scales with the strength of the built-in electric field of the polar material, and is immediately understandable in terms of an electronic reconstruction at the nonpolar-polar interface. These results thus conclusively identify the polar-catastrophe model as the intrinsic origin of the doping at this polar oxide interface.