FLUX CREEP AND TRANSPORT CRITICAL CURRENT-DENSITY IN HIGH-TC SUPERCONDUCTORS

The transport critical current density Jc of thin films and bulk ceramic specimens of high-Tc superconductors has been measured as a function of temperature in the range 4.2 K to Tc under self-field conditions. Theoretical models for thermally activated flux creep in homogeneous superconductors, and for current transport across Josephson weak links (S-I-S and S-N-S junctions) are used to analyze the temperature dependence of Jc. Although it is possible to prepare specimens showing weak link behaviour, we find that flux creep determines the critical current density of both oriented films having Jc(0) = 103 to 106 A/cm2 and bulk specimens having Jc(0) ≥ 103 A/cm2. In these specimens Jc(T) increases approximately linearly with decreasing temperature for t ≤ 0.7 (where t = T/Tc). Theoretical fits to the data are obtained using a pinning energy or barrier potential U(0) = 10kTc- 65-90 meV. © 1990.