EVIDENCE THAT PAIR-BREAKING AT THE GRAIN-BOUNDARIES OF BI2SR2CA2CU3OX TAPES DETERMINES THE CRITICAL-CURRENT DENSITY ABOVE 10-K IN HIGH MAGNETIC-FIELDS

The critical current density of an aligned Ag doped Bi2Sr2Ca2Cu3Ox, tape has been measured from 10 K up to T-c (105 K) in magnetic fields up to 15 T. Measurements of the critical current density (J(c)(B, T)) have been completed for three different configurations of magnetic field, transport current, and superconducting tape: (i) J perpendicular to c axis, J perpendicular to B, and B perpendicular to c axis; (ii) J perpendicular to c axis, J perpendicular to B, and B parallel to c axis; (iii) J perpendicular to c axis, J parallel to B, and B perpendicular to c axis. In all three configurations at high magnetic fields up to 15 T, we find the critical current density can be described by J(c)(B, T) = alpha(phi, T) exp[-mu(0)H/beta(phi, T)] where beta(phi, T) is of a separable variable form beta(phi, T) = beta(#)(T)/f(phi) where beta(#)(T) is a function of temperature alone and f(phi) is a constant dependent only on the orientation of B, J, and the c axis. A similar but not identical exponential magnetic field dependence has been found in Bi2Sr2Ca2Cu3Ox, Bi2Sr2CaCu2Ox, and YBa2Cu3Oy thin films. We discuss the evidence that the exponential magnetic field dependence suggests that a pair breaking mechanism operates at barriers in these materials. We conclude that the grain boundaries determine J(c)(B, T) in the Bi2Sr2Ca2Cu3Ox textured tape.