A New Method to Obtain U(J) Relationship in High Temperature Superconductor

Abstract

An implicit expression for the time dependence of the current density J(t) is derived without the constant assumption of dU/dJ or <dU/dJ>, based on which a new method to extract U(J) relationship from magnetic relaxation data in high temperature superconductors is described. This method is applied to a melt textured growth YBa2Cu3O6+x sample and we obtain U(J)~ J-μ with μ=0.90 for H‖c, which is in accordance with that derived by the usual method suggested by Malery et al.(μ=0.87). Moreover, both methods give the same value of the constant C, which implies that the determination of C by the requirement of continuity of the U(J) curve at different temperatures is reliable. And the results U(J)~ J-μ by both methods are evidence for the collective pinning or the vortex glass theory.