Surface critical currents and activation energies in high-temperature superconductors

Abstract

The critical currents and activation energies related to the surface (Bean-Livingston) barrier are found for high-temperature superconductors. It is shown that the surface barrier does not undergo a temperature (exponential) suppression which is typical of the bulk pinning. Therefore the surface irreversibility dominates over the bulk one at high temperatures T ≌ T c, where the bulk pinning is suppressed by thermal fluctuations. The dependencies of the surface activation energies U surf on the external field ( U surf H − 1 2 ) and transport current ( U surf J − 1 2 for moderate currents) prove to be different from those for U bulk . This helps to distinguish between the surface and bulk effects on the transport and magnetization properties of HTSC. The interplay between the surface and the bulk contribution is discussed.