CURRENT DEPENDENCE OF PINNING ENERGY AND FLUX DYNAMICS IN HIGH-TEMPERATURE SUPERCONDUCTORS

We show that the usually observed logarithmic U(J) dependence at large magnetic fields is related to the increasing number of free flowing v ortices distributed in the weak pinning centers, with respect to the v ortices in the strong pinning centers in the flux creep regime. Increa sing the flux density (i.e. increasing the external magnetic field) th e flux distribution on the pinning centers has a larger dispersion (si gma u much greater than k(B)T) and this leads to a logarithmic U(J) be havior. The comparison with the experimental data seems to prove this idea.