Depinning current for flux lines in Ag/BSCCO superconducting tapes

Voltage-current characteristics were measured for Ag-clad (Bi, Pb)2Sr2Ca2Cu3O10 multifilamentary samples at 77 K, with magnetic field H parallel to the c-axis. The data were fitted by V=V0 exp[-(l*/l)μ], where l is the critical current with no thermal excitations. The parameter μ was obtained from logd(In V)/d/3] versus log l 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 I0 log y0). The values of mu for these fields were O< mu <1. The convergence is a new experimental result, not contained in any of the existing models. It gives l0, which is the depinning current in the extrapolation to zero field. It was found that l0/lc1μvcm-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. (author)