ORIGIN OF THE FINITE CRITICAL-CURRENT DENSITY OF HIGHLY ANISOTROPIC BI2SR2CA2CU3OX AG TAPES IN ZERO EXTERNAL MAGNETIC-FIELD/

The current-voltage characteristics of highly anisotropic Bi2Sr2Ca2Cu3 Ox/Ag tapes (short samples) were investigated in a large temperature i nterval, down to 25 K below the critical temperature, in zero external magnetic field. For samples with a relatively low self-field critical -current density (of the order of 10(3) A/cm(2) at 77 K), the inter- a nd intragranular contributions to the dissipation process were clearly separated. The I-V curve shape indicates the existence of finite inte r- and intragranular critical currents. The anisotropy of the intergra nular critical current in weak applied magnetic fields revealed good a greement with the ''railway switch'' model for the preferred transport current path. It was shown that, in the case of a large anisotropy, t he finite zero-field critical-current density at high temperatures ori ginates from a size limitation of the two-dimensional vortex fluctuati ons. This size limitation is caused by the finite (a, b) plane extensi on of the microscopic current path.