Depinning current for flux lines in Ag/BSCCO superconducting tapes

Voltage-current characteristics were measured for Ag-clad (Bi, Pb)(2)Sr2Ca2Cu3O10 multifilamentary samples at 77 K, with magnetic field H parallel 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 parameter 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 the 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 convergence is a new experimental result, not contained in any of the existing models. It gives l(0), which is the depinning current in the extrapolation 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 enables a clear distinction of the ranges of H for different dissipation regimes.