Profiling the interface electron gas of LaAlO3/SrTiO3 heterostructures by hard X-ray photoelectron spectroscopy

TL;DR

This study uses hard X-ray photoelectron spectroscopy to analyze the electron gas at LaAlO3/SrTiO3 interfaces, revealing a thin electron layer and linking electronic reconstruction to conductivity and superconductivity.

Contribution

It provides direct spectroscopic evidence of the electron gas thickness and its variation with LaAlO3 layers, supporting the electronic reconstruction mechanism.

Findings

Electron gas thickness is less than 4 nm.

Carrier density increases with more LaAlO3 layers.

Electronic reconstruction drives interface conductivity.

Abstract

The conducting interface of LaAlO$_3$/SrTiO$_3$ heterostructures has been studied by hard X-ray photoelectron spectroscopy. From the Ti~2$p$ signal and its angle-dependence we derive that the thickness of the electron gas is much smaller than the probing depth of 4 nm and that the carrier densities vary with increasing number of LaAlO$_3$ overlayers. Our results point to an electronic reconstruction in the LaAlO$_3$ overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the Berezinskii-Kosterlitz-Thouless type.