c-axis I-V characteristics in highly c-axis-oriented (Bi,Pb)₂Sr₂Ca₂Cu₃O_x silver-sheathed tapes

We have measured c-axis I-V characteristics of highly c-axis-oriented (Bi,Pb)₂Sr₂Ca₂Cu₃O_x silver-sheathed tapes (Bi2223/Ag) in the field H ≤ 0.5 T near T_c (80 to 110 K). The Josephson junction effect is observed. In each I-V curve a voltage jump V₀ is clearly found which may correspond to the transition from states with Cooper tunneling to states with quasi-particle tunneling. This implies the Josephson coupling between the grains or between the CuO₂ tri-layers in Bi2223/Ag tapes along the c-direction. The temperature dependence of the superconducting gap Δ(T) can be successfully scaled to that obtained from BCS theory. The gap Δ does not depend much on a magnetic field of H ≤ 0.5 T for H ∥ c. The voltage jumps observed in the experiments are not as steep as in a single SIS junction, which may originate from the variety of junctions in Bi2223/Ag tapes or the thermal fluctuation.