Anomalous independence of interface superconductivity from carrier density.

The recent discovery of superconductivity at the interface of two non-superconducting materials has received much attention. In cuprate bilayers, the critical temperature (Tc) can be significantly enhanced compared with single-phase samples. Several explanations have been proposed, invoking Sr interdiffusion, accumulation and depletion of mobile charge carriers, elongation of the copper-to-apical-oxygen bond length, or a beneficial crosstalk between a material with a high pairing energy and another with a large phase stiffness.

Evidence for a high-temperature disorder-induced mobility in solid 4He.

We have carried out torsional oscillator experiments on solid 4He at temperatures between 1.3 K and 1.9 K.