Increase of the critical current in single-crystal Bi2Sr2CaCu2O8-δ with ion-induced flux-pinning sites

Single crystals of Bi2Sr2CaCu2O8-δ were irradiated with 50-MeV O+616 along the c axis. Using a single coil as a noncontact probe, the transition temperature and the critical current of the samples were measured in situ as a function of total beam fluence. We observe an increase and a subsequent decrease in the critical current at 60, 75, and 80 K with a peak corresponding to fluences of ∼1×1013 ions/cm2. Up to this fluence the transition temperature remained a constant. Higher fluences caused a decrease in both the transition temperature and the critical current. The results are discussed in terms of a simple model assuming the ion-induced defects cause flux pinning sites.