Magnetic-Field-Enhanced Superconductivity in Au/Ge Layered Films

Abstract

Temperature dependences of parallel and perpendicular critical fields have been measured for layered superconductors of Au/Ge. Sandwiched films with a single ultrathin Au layer ranging in thickness from 1.0 to 2.0 nm exhibit superconductivity with a large anisotropy of critical fields below 0.6∼0.8 K. For films with a Au-thickness around 1.0 nm, the critical temperature is enhanced above the zero-field critical temperature by applying a parallel magnetic field. For thicker films, the enhancement of superconductivity due to magnetic field is also observed as a concave temperature dependence of squared parallel critical fields, deviating from that obtained from the Ginzburg-Landau theory.