(111) interfaces*

The unique electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. One prominent example is the emergence of a superconducting electron gas at the interface of LaAlO₃/SrTiO₃. 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 IV measurements indicate that the superconductivity is two dimensional. Low carrier density EuO/KTaO₃(111) samples, with higher mobilities, show spontaneous in-plane transport anisotropy at temperatues prior to the onset of global superconductivity, suggesting the emergence of a 'stripe' phase where the superconductivity is nearly homogeneous in one direction, but modulated in the other.
Reference: C. Liu et al., arXiv:2004.07416