Magnetization Measurements and Ginzburg-Landau Simulations of Micron-Size β-Tin Samples:Evidence for an Unusual Critical Behavior of Mesoscopic Type-I Superconductors

摘要

We describe investigations of the largely unexplored field of mesoscopic type-I superconductors. Micromagnetometry and 3D Ginzburg-Landau simulations of our single crystal β-tin samples in this regime reveal size- and temperature-dependent supercritical fields whose behavior is radically different from the bulk critical field H_C~B. We find that complete suppression of the intermediate state in medium-size samples can result in a surprising reduction of the critical field significantly below H_C~B. We also reveal an evolution of the superconducting-to-normal phase transition from the expected irreversible first order at low temperatures through the previously unobserved reversible first-order to a second-order transition close to T_C, where the critical field can be many times larger than H_C~B. Finally, we have identified striking correlations between the mesoscopic H_(c3) for nucleation of surface superconductivity and the thermody-namic H_C near T_C. All these observations are entirely unexpected in the conventional type-I picture.