Discovery of two-dimensional anisotropic superconductivity at KTaO₃ (111) interfaces

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 KTaO₃ and insulating overlayers of either EuO or LaAlO₃. The superconducting transition temperature, approaching 2.2 K, is about one order of magnitude higher than that of the LaAlO₃/SrTiO₃ system. Strikingly, similar electron gases at (001) KTaO₃ interfaces remain normal down to 25 mK. The critical field and current-voltage measurements indicate that the superconductivity is two dimensional. Higher mobility EuO/KTaO₃ (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.