Angular Dependence of the Current-Voltage Characteristics of Bi-Sr-Ca-O in a Magnetic Field

We report on the detailed angular dependence of the resistive transition in single crystal and thin film Bi-Sr-Ca-Cu-O as a function of applied field, current and temperature. In single crystals the observed onset of resistance for small values of the applied field (100 Oe) even at low current densities (10 A/cm sup 2) suggests that the transition is more indicative of flux flow effects than of the upper critical field. Therefore, (unlike YBCO) the angular dependence of the magnetic-field-induced resistive transition cannot be fit by any standard model for anisotropic critical fields in superconductors. The anisotropic ratios are as large as 50 for fields applied parallel and perpendicular to the c-axis of the crystal, indicating large differences in the viscosity for flux motion in the two directions.