FLUX-CREEP DISSIPATION IN EPITAXIAL YBA2CU3O7-DELTA FILM - MAGNETIC-FIELD AND ELECTRICAL-CURRENT DEPENDENCE

We have investigated the dissipation characteristics in the mixed state of YBa2Cu3O7-delta film, grown epitaxially on the SrTiO3(100) substrate, in terms of external transport current as well as magnetic field applied parallel to the c axis of the film. The dissipation fits well the thermally activated flux creep model, R = R0 exp(-U/k(B)T), where U is a function of electrical current, magnetic field, and temperature. In the range of current density approximately 20-4000 A/cm2, the current dependence of the activation energy U scales with ln(I/I0), as observed recently by Zeldov et al. U shows a power-law dependence on magnetic field as H-beta with beta = 0.73 +/- 0.002. We obtain the resistance prefactor R0 proportional to the applied magnetic field, provided the Ginzburg-Landau-type magnetic-field suppression of the mean-field transition temperature T(c)0 is taken into account. In addition, we present the magnetoresistance at various temperatures below T(c)0, in good accordance with the flux-creep model.