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

Phys Rev Lett. 2006 Feb 24;96(7):077003. doi: 10.1103/PhysRevLett.96.077003. Epub 2006 Feb 23.


We report specific heat measurements on neutron-irradiated MgB2 samples, for which the critical temperature is lowered to 8.7 K, 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 21 K, while single-gap superconductivity is well established as a bulk property, not associated with local disorder fluctuations, when Tc decreases to 11 K.