Observation of the crossover from two-gap to single-gap superconductivity through specific heat measurements in neutron-irradiated MgB2

Abstract

We report specific heat measurements on neutron-irradiated MgB2 samples, for which the critical temperature is lowered to 8.7K, but the superconducting transition remains extremely sharp, indicative of a defect structure extremely homogeneous. Our results evidence the presence of two superconducting gaps in the temperature range above 21K, while single-gap superconductivity is well established as a bulk property, not associated with local disorder fluctuations, when Tc decreases to 11K. © 2006 The American Physical Society.