Flux creep and transport critical current density in high-T c superconductors

Abstract

The transport critical current density J c of thin films and bulk ceramic specimens of high- T c superconductors has been measured as a function of temperature in the range 4.2 K to T c 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 J c. 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 J c (0) = 10 3 to 10 6 A/ cm 2 and bulk specimens having J c(0) ≥ 10 3 A/cm 2. In these specimens J c( T) increases approximately linearly with decreasing temperature for t ≤ 0.7 (where t = T/ T c). Theoretical fits to the data are obtained using a pinning energy or barrier potential U(0) = 10 kT c- 65–90 meV.