Using specific heat to scan gaps and anisotropy of MgB2

We performed specific heat measurements to study the superconducting properties of the similar to40 K superconductor MgB2, up to 16 T, using polycrystal and single crystal samples. Our results establish the validity of the two-gap model. We tested the effect of disorder by irradiating our sample. This procedure decreased T-c down to similar to26 K, but did not suppress completely the smaller gap, at variance with theoretical expectations. A positive effect of the irradiation was the increase of H-c2 up to almost 30 T. Our results on the single crystal allow the anisotropy of each band to be determined independently, and show the existence of a cross-over field well below H-c2 characterizing the physics of the small-gapped band. We also present preliminary results on Nb3Sn, showing similar, but weaker effects. (C) 2004 Elsevier B.V. All rights reserved.