Observation of the gap merging in neutron irradiated MgB2

We measure specific heat on neutron-irradiated MgB2 samples, whose critical temperature is reduced down to 8.7 K keeping the superconducting transition extremely sharp. The results clearly show the present of two superconducting gap in the range of temperature between 39 and 21 K, whereas a single gap behavior is observed when T-c is lower than 11 K. (c) 2007 Elsevier B.V. All rights reserved.