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

Single crystals of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ were irradiated with 50-MeV $^{16}\mathrm{O}^{+6}$ 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 \ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ions/${\mathrm{cm}}^{2}$. 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.