A study was made of the effect of disorder on the superconducting properties of polycrystalline MgB2 by specific-heat measurements. In the pristine state, these measurements gave a bulk confirmation of the presence of 2 superconducting gaps with 2Δ0/kBTC = 1.3 and 3.9 with almost equal weights. The scattering introduced by irradiation suppressed TC and tended to average the 2 gaps although less than predicted by theory. It was also found that, by suitable irradiation with fast neutrons, a substantial bulk increase of dHC2/dT at TC could be obtained without sacrificing more than a few degrees in TC. The upper critical field of the sample after irradiation exceeded 28T as T → 0.

Specific Heat of MgB2 after Irradiation. Y.Wang, F.Bouquet, I.Sheikin, P.Toulemonde, B.Revaz, M.Eisterer, H.W.Weber, J.Hinderer, A.Junod: Journal of Physics - Condensed Matter, 2003, 15, 883-93