THERMALLY ACTIVATED FLUX MOVEMENT AND CRITICAL TRANSPORT CURRENT-DENSITY IN EPITAXIAL BI2SR2CACU2O8+DELTA FILMS

In this article we report on thermally excited flux creep and the critical transport current density j(c), in high-quality epitaxial Bi2Sr2CaCu2O8+delta thin films. Both dissipative mechanisms are governed by the highly anisotropic behavior of this compound which was investigated by means of the angular dependence of the magnetoresistivity (gamma greater-than-or-equal-to 150). The activation energy U for thermally excited flux creep was evaluated with respect to temperature, magnetic field, and applied current density j. U(TB,j) is essentially increasing linearly with falling temperature, power-law dependent on the field (U is-proportional-to B(-alpha) with alpha almost-equal-to 0.5), and almost independent of current density for j less-than-or-equal-to 10(5) angstrom/cm2. These experimental results are consistent with the concept of plastic flux creep. The critical current density exhibits high absolute values [j(c)(77 K,B=0)=4X10(5) angstrom/cm2] and was measured for magnetic fields in the configuration B parallel-to c up to 10 T and also with respect to various THETA angles between the c axis and field direction. The decrease of j(c), with increasing B was found to be significantly reduced in comparison to single crystals and prior results on thin films. A further enhancement in the j(c) (B,T) behavior could not be achieved by chemical doping through partial substitution of copper by zinc.