Superfluid stiffness of a KTaO3-based two-dimensional electron gas

TL;DR

This study demonstrates gate-tunable superconductivity with a large gap and Berezinsky-Kosterlitz-Thouless transition in a KTaO3-based 2DEG, revealing new physics and potential applications in oxide interfaces.

Contribution

It reports the discovery of superconductivity in (111)-oriented KTaO3 2DEGs with unique properties not observed in SrTiO3 interfaces.

Findings

Gate-tunable superconductivity observed.

Large superconducting gap exceeding BCS predictions.

Evidence of Berezinsky-Kosterlitz-Thouless transition.

Abstract

After almost twenty years of intense work on the celebrated LaAlO3/SrTiO3 system, the recent discovery of a superconducting two-dimensional electron gases (2-DEG) in (111)-oriented KTaO3-based heterostructures injects new momentum to the field of oxides interfaces. However, while both interfaces share common properties, experiments also suggest important differences between the two systems. Here, we report gate tunable superconductivity in 2-DEGs generated at the surface of a (111)-oriented KTaO3 crystal by the simple sputtering of a thin Al layer. We use microwave transport to show that (111)-KTaO3 2-DEGs exhibit a node-less superconducting order parameter with a gap value significantly larger than expected within a simple BCS weak-coupling limit model. Consistent with the two-dimensional nature of superconductivity, we evidence a well-defined Berezinsky-Kosterlitz-Thouless type of transition, which was not reported on SrTiO3-based interfaces. Our finding offers innovative perspectives for fundamental science but also for device applications in a variety of fields such as spin-orbitronics and topological electronics.