Critical current in polycrystalline Bi-Ca-Sr-Cu-O films

Thin films of Bi-Ca-Sr-Cu-O were prepared by rf magnetron sputtering a sintered ${\mathrm{Bi}}_2$ ${\mathrm{CaSr}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{8\mathrm{-}\mathrm{y}}$ target. The films were deposited on a MgO(100) substrate. The data reported here have a $T_c$ (50%) of about 86 K and a transition width Δ$T_c$=90–81 K (90%–10%). Temperature-dependent I-V characteristics examined over wide ranges reveal that the critical current is proportional to (1-T/$T_c$ ${)}^{3/2}$ near $T_c$. The implication of the (3/2 power dependence will be discussed.