Oxide tunnel junctions supporting a two-dimensional electron gas

TL;DR

This paper investigates oxide heterostructures with 2DEGs as tunneling barriers, revealing enhanced conductance via resonant tunneling influenced by orbital polarization and lattice effects, opening new avenues for out-of-plane oxide nanoelectronics.

Contribution

It demonstrates the formation of a 2DEG within oxide tunnel barriers and its impact on tunneling conductance, highlighting the role of orbital polarization and lattice polarization effects.

Findings

Resonant tunneling significantly enhances conductance.

Orbital polarization determines tunneling selectivity.

Lattice polarization influences tunneling behavior.

Abstract

The discovery of a two-dimensional electron gas (2DEG) at the interface between insulating oxides has led to a well-deserved level of excitement due to possible applications as "in-plane" all-oxide nanoelectronics. Here we expand the range of possibilities to the realm of "out-of-plane" nanoelectronics by examining such all-oxide heterostructures as barriers in tunnel junctions. As an example system we perform first-principles electronic structure and transport calculations of a tunnel junction with a [SrTiO3]4/[LaO]1/[SrTiO3]4 heterostructure tunneling barrier embedded between SrRuO3 electrodes. The presence of the LaO atomic layer induces the formation of a 2DEG within the tunneling barrier which acts as an extended defect perpendicular to the transport direction, providing a route for resonant tunneling. Our calculations demonstrate that the tunneling conductance in this system can be strongly enhanced compared to a pure SrTiO3 barrier due to resonant tunneling, but that lattice polarization effects play a significant role in determining this behavior. In addition we find that this resonant tunneling is highly selective of the orbital symmetry of the tunneling states due to the "orbital polarization" of the 2DEG. We also discuss how the properties of the 2DEG are affected by the presence of metal electrodes.