Current-voltage characteristics in the vicinity of the fishtail peak in YBa2Cu3O6.95 single crystals

Current-voltage characteristics (CVC's) of YBa2Cu3O6.95 single crystal were measured for dc-current densities up to 3 x 10(4) A/cm(2). The depinning c ritical current J(cd) was estimated within the Bardeen-Stephen model and no anomalous behavior was observed in J(cd)(H) in contrast to the fishtail be havior of the critical current J(cE) determined on the electric field level E = const. Assuming that E proportional to exp[-(U/kT)(J(ed)/J)(mu)], the field dependence of the activation energy U and of the exponent mu were der ived. The minimum in J(cE)(H) is shown to correspond to a crossover from si ngle vortex to small bundle creep, whereas the maximum in J(cE)(H) correspo nds to a crossover from elastic to plastic creep. (C) 1999 Elsevier Science B.V. All rights reserved.