Superconductivity of Nb3Sn, Nb, V, Pb and Sn after low temperature irradiation with 25 MeV oxygen ions

The critical temperature Tc and transition width Tϑ of the superconductors were measured as functions of fluence and subsequent annealing. For the transition metals Nb, V and the nontransition metals Pb, Sn radiation induced resistivity ΔρB and damage rates were determined up to high fluences at irradiation temperatures T ⩽ 20 K and T ⩽ 7.2 K, respectively. Measurements of the critical current density jc(B, T) of 5 μm Nb3Sn samples (CVD) were made and Bc2, the volume pinning force density PV and scaling law were deduced. The Tc levelling off on Nb3Sn at high fluences was especially studied. In Nb an enhancement of Tc was observed and both Nb and V showed a significant broadening of Tϑ in heavily damaged state. Pb and Sn are discussed with respect to smoothing out of the anisotropy and to changes of the electron-phonon coupling strength α2 (w) and phonon spectrum F(w). Different behaviour of Tc vs. ΔρB between irradiation and annealing was observed in Nb, V and Pb, but not Sn.