Band inversion driven by electronic correlations at the (111) LaAlO$_3$/SrTiO$_3$ interface

TL;DR

This study reveals that at (111) LaAlO$_3$/SrTiO$_3$ interfaces, electronic correlations induce a band inversion affecting orbital contributions, leading to unique transport properties and strong spin-orbit coupling with minimal electrostatic control.

Contribution

It demonstrates that electronic correlations cause band inversion at (111) LAO/STO interfaces, influencing orbital contributions and transport behavior, a novel insight compared to (001) interfaces.

Findings

Transport involves two electron-like sub-bands with non-monotonic carrier density.

Band inversion driven by Coulomb interactions affects orbital contributions.

Strong spin-orbit coupling with reduced electrostatic modulation observed.

Abstract

Quantum confinement at complex oxide interfaces establishes an intricate hierarchy of the strongly correlated $d$-orbitals which is widely recognized as a source of emergent physics. The most prominent example is the (001) LaAlO$_3$/SrTiO$_3$(LAO/STO) interface, which features a dome-shaped phase diagram of superconducting critical temperature and spin-orbit coupling (SOC) as a function of electrostatic doping, arising from a selective occupancy of $t_{2g}$ orbitals of different character. Here we study (111)-oriented LAO/STO interfaces - where the three $t_{2g}$ orbitals contribute equally to the sub-band states caused by confinement - and investigate the impact of this unique feature on electronic transport. We show that transport occurs through two sets of electron-like sub-bands, and the carrier density of one of the sets shows a non-monotonic dependence on the sample conductance. Using tight-binding modeling, we demonstrate that this behavior stems from a band inversion driven by on-site Coulomb interactions. The balanced contribution of all $t_{2g}$ orbitals to electronic transport is shown to result in strong SOC with reduced electrostatic modulation.