Superfluid stiffness of a KTaO ₃-based two-dimensional electron gas

Abstract

After almost twenty years of intense work on the celebrated LaAlO ₃/SrTiO ₃system, the recent discovery of a superconducting two-dimensional electron gas (2-DEG) in (111)-oriented KTaO ₃-based heterostructures injects new momentum to the field of oxides interface. 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 KTaO ₃ crystal by the simple sputtering of a thin Al layer. We extract the superfluid stiffness of the 2-DEGs and show that its temperature dependence is consistent with a node-less superconducting order parameter having a gap value larger than expected within a simple BCS weak-coupling limit model. The superconducting transition follows the Berezinskii-Kosterlitz-Thouless scenario, which was not reported on SrTiO ₃-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.

Abstract

Heterostructures based on (111)-oriented KTaO ₃crystals are a new platform for studying oxide interfaces. Gate-tunable superconductivity in 2D electron gases at the surface of (111)-oriented KTaO ₃is now reported, with the superconducting transition being of the Berezinskii-Kosterlitz-Thouless type.