Discovery of two-dimensional anisotropic superconductivity at KTaO$_3$ (111) interfaces

TL;DR

This paper reports the discovery of two-dimensional anisotropic superconductivity at (111) KTaO$_3$ interfaces with EuO or LaAlO$_3$, showing higher transition temperatures and unique anisotropic properties compared to other interfaces.

Contribution

It demonstrates superconductivity at (111) KTaO$_3$ interfaces with higher transition temperatures and anisotropic features, revealing new quantum states at these interfaces.

Findings

Superconductivity with T_c up to 2.2 K at (111) KTaO$_3$ interfaces.

Anisotropic transport properties indicating stripe-like phase.

Superconductivity is two-dimensional and distinct from (001) interfaces.

Abstract

The unique electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. Here we observe superconductivity in electron gases formed at interfaces between (111) oriented KTaO$_3$ and insulating overlayers of either EuO or LaAlO$_3$. The superconducting transition temperature, approaching 2.2 K, is about one order of magnitude higher than that of the LaAlO$_3$/SrTiO$_3$ system. Strikingly, similar electron gases at (001) KTaO$_3$ interfaces remain normal down to 25 mK. The critical field and current-voltage measurements indicate that the superconductivity is two dimensional. Higher mobility EuO/KTaO$_3$ (111) samples show a large in-plane anisotropy in transport properties at low temperatures prior to onset of superconductivity, suggesting the emergence of a stripe like phase where the superconductivity is nearly homogeneous in one direction, but strongly modulated in the other.