EXPONENTIAL DECAY OF CRITICAL CURRENT IN Y-BA-CU-O - RELATIONSHIP WITH THE PINNING POTENTIAL PROFILE AND ITS PHYSICAL ORIGIN

An exponential decay of critical current density has been reported by several authors for high-temperature superconductors in the configuration H parallel-to c. In order to give an interpretation of this behavior, we suggest that it is related to a specific profile of the pinning potential U(p)(R) acting on the vortices. For planar defects, consideration of the kinetic energy associated with supercurrents flowing around the vortex core leads to a logarithmic dependence of U(p)(R). We then follow the general hypothesis of flux creep models with non-linear U(p)(R), in the limit of direct summation for the elementary pinning forces. In this framework, we show that a logarithmic dependence of the pinning potential on the defect-vortex distance leads to the experimentally observed critical current decay. Low-temperature values of the critical current density and of the V(c)X product (the "movable volume" times the pinning potential width) obtained in Y-Ba-Cu-O compounds are analyzed in this model from a qualitative point of view.