Ballistic transport through quantum point contacts of multi-orbital oxides

TL;DR

This paper investigates ballistic transport in oxide-based quantum point contacts at the LaAlO3/SrTiO3 interface, revealing three distinct regimes influenced by orbital sub-bands, magnetic fields, and spin-orbit coupling, aligning well with experimental data.

Contribution

It provides a detailed theoretical analysis of multi-orbital quantum transport in oxide interfaces, highlighting the role of orbital mixing, magnetic fields, and spin-orbit effects in conductance quantization.

Findings

Robust conductance quantization at low energies involving d_{xy} sub-bands

Magnetic field suppresses sub-band splitting at intermediate energies

Strong orbital mixing causes narrow conductance plateaus at higher energies

Abstract

Linear and non-linear transport properties through an atomic-size point contact based on oxides two-dimensional electron gas is examined using the tight-binding method and the $\mathbf{k\cdot p}$ approach. The ballistic transport is analyzed in contacts realized at the (001) interface between band insulators $LaAlO_3$ and $SrTiO_3$ by using the Landauer-B\"uttiker method for many sub-bands derived from three Ti 3d orbitals ($d_{yz}$, $d_{zx}$ and $d_{xy}$) in the presence of an out-of-plane magnetic field. We focus especially on the role played by the atomic spin-orbit coupling and the inversion symmetry breaking term pointing out three transport regimes: the first, at low energies, involving the first $d_{xy}$-like sub-bands, where the conductance quantization is robust; a second one, at intermediate energies, entailing further $d_{xy}$-like sub-bands, where the sub-band splitting induced by the magnetic field is quenched; the third one, where the mixing between light $d_{xy}$-like, heavy $d_{yz}$-like and $d_{zx}$-like sub-bands is so strong that the conductance plateaus turn out to be very narrow. Very good agreement is found with recent experiments exploring the transport properties at low energies.