Evidence that pair breaking at the grain boundaries of Bi2Sr2Ca2Cu3Oxtapes determines the critical current density above 10 K in high magnetic fields

The critical current density of an aligned Ag doped Bi 2 Sr 2 Ca 2 Cu 3 O x 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//c axis; (iii) J perpendicular to c axis, J//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 /sup /(T)/f( phi ) where beta /sup /(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 Bi 2 Sr 2 Ca 2 Cu 3 O x , Bi 2 Sr 2 CaCu 2 O x and YBa 2 Cu 3 O x , 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 Bi 2 Sr 2 Ca 2 Cu 3 O x textured tape.