DEPINNING CURRENT FOR FLUX LINES IN AG BSCCO SUPERCONDUCTING TAPES/

Voltage-current characteristics were measured for Ag-clad (Bi, Pb)(2)S r2Ca2Cu3O10 multifilamentary samples at 77 K, with magnetic field H pa rallel to the c-axis. The data were fitted by V = V-0 exp[-(l/l)(mu)] , where I is the critical current with no thermal excitations. The pa rameter mu was obtained from log[d(ln V)/dl] versus log I plots, where the data give straight lines for each of the fields. The lines for th e fields 30 mT < H < 350 mT converge at a characteristic point (log/(0 ), log y(0)). The values of mu for these fields were 0 < mu < 1. The c onvergence is a new experimental result, not contained in any of the e xisting models. It gives l(0), which is the depinning current in the e xtrapolation to zero field. It was found that l(0)/l(c)(1 mu Vcm-1) = 3.2 +/- 0.4 at H = 0 for all Bi(2223) samples measured. Our analysis e nables a clear distinction of the ranges of H for different dissipatio n regimes.