Superconductivity and frozen electronic states at the (111) LaAlO₃/SrTiO₃ interface

In spite of Anderson’s theorem¹, disorder is known to affect superconductivity in conventional s-wave superconductors^2–11. In most superconductors, the degree of disorder is fixed during sample preparation. Here we report measurements of the superconducting properties of the two-dimensional gas that forms at the interface between LaAlO₃ (LAO) and SrTiO₃ (STO) in the (111) crystal orientation, a system that permits in situ tuning of carrier density and disorder by means of a back gate voltage V_g. Like the (001) oriented LAO/STO interface^12–15, superconductivity at the (111) LAO/STO interface can be tuned by V_g. In contrast to the (001) interface, superconductivity in these (111) samples is anisotropic, being different along different interface crystal directions, consistent with the strong anisotropy already observed other transport properties at the (111) LAO/STO interface^16,17. In addition, we find that the (111) interface samples “remember” the backgate voltage V_F at which they are cooled at temperatures near the superconducting transition temperature T_c, even if V_g is subsequently changed at lower temperatures. The low energy scale and other characteristics of this memory effect (< 1 K) distinguish it from charge-trapping effects previously observed in (001) interface samples.