Morphology of defects and the transport properties of high-Tc superconductors

The distribution of the pinning energies f(E) at low temperatures for polycrystalline Bi-2212 thin rods were recently determined from experimental measurements using an inversion scheme. An analysis is proposed to calculate the same distributions for the same samples directly with few simple assumptions. This approach depends on the fact that in the long time limit, the magnetization relaxation behavior is controlled by the diffusion coefficient D of the local vortex lines. The diffusion coefficient has a temperature and field dependence which influences the relaxation time constants of the magnetization curves. The calculated distributions also take into account the effects of the thermal driving forces on the vortex dynamics and consequently on the transport properties. Excellent agreements between the measurements and the model predictions indicate that the proposed distribution of the activation energy is consistent with those determined from the experimental measurements using inversion methods. (C) 2001 Elsevier Science B.V. All rights reserved.