ON THE DISSIPATION PROCESS IN BI2SR2CA2CU3O10 TAPES AND BULK SAMPLES WITH PREFERENTIAL GRAIN-ORIENTATION IN ZERO EXTERNAL MAGNETIC-FIELD

Current-voltage characteristics of Bi2Sr2Ca2Cu3O10 tapes and bulk samp les with preferentially oriented crystallites have been measured in ze ro applied magnetic field and for temperatures close to the mean-field critical-temperature, T-c0. It was shown that the power-law dependenc e, V = Al-a, valid for two-dimensional systems, does not correctly des cribe the data, which clearly indicate the existence of a finite criti cal-current density, J(c). The experimental I-V curves are fitted quit e well with the model which attributes the finite critical-current den sity to the coupling between the CuO2 double layers. It was found that J(c) vanishes at a temperature value below T-c0. This behavior can re sult from the occurrence of vortex fluctuation-induced layer decouplin g and/or from the contribution of entropy to the vortex unbinding proc ess.