IRRADIATION ENHANCEMENT OF SUPERCONDUCTIVITY. A MULTIHARMONIC STUDY ê

We have found in multiharmonic magnetic susceptibility experiments that neutron irradiation of high temperature superconductors produces a depression of the superconducting characteristics (critical temperature and Meissner screening) at moderate fluence 0.98 × 1017 neutrons/cm2 and an unexpected enhancement of the intragranular superconducting properties at 9.98 × 1017 neutrons/cm2. In contrast, the intergranular properties support a continuous suppression. We assume that this behavior is the result of the change of the nature of defect distribution at high fluence, when the uniform distribution of defects starts to develop space instabilities as a result of the subtle interplay of the in-cascade rate of interstitial loops production, cascade collapse of the vacancy loops, and the excess network bias.