Neutron irradiation of sputtered NbN films

The authors report neutron irradiation experiments on sputtered NbN films, up to a fluence of 10²³ m^-2 (E> 0.1 MeV), which prove that NbN films are also extremely radiation-hard high-field superconductors. Both the transition temperatures, T_c, and the normal state resistivities show only small changes with neutron fluence. Concerning the critical current densities, j_c, degradations by as much as 30% are observed at low fields, whereas in an intermediate field range (11-15 T), virtually no change of j_c is seen, and at high fields (near 20 T), even an increase of j_c is found. The latter observation is ascribed to a radiation-induced increase of the upper critical field, B_c2, and to the occurrence of peak effects near B_c2