Thermally activated flux movement and critical transport current density in epitaxial Bi2Sr2CaCu2O8+ delta films.

Abstract

In this article we report on thermally excited flux creep and the critical transport current density [ital j][sub [ital c]] in high-quality epitaxial Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+[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][ge]150). The activation energy [ital U] for thermally excited flux creep was evaluated with respect to temperature, magnetic field, and applied current density [ital j]. [ital U]([ital T],[ital B],[ital j]) is essentially increasing linearly with falling temperature, power-law dependent on the field ([ital U][proportional to][ital B][sup [minus][alpha]] with [alpha][approx]0.5), and almost independent of current density for [ital j][le]10[sup 5] A/cm[sup 2]. These experimental results are consistent with the concept of plastic flux creep. The critical current density exhibits high absolute values [[ital j][sub [ital c]](77 K, [ital B]=0)=4[times]10[sup 5] A/cm[sup 2]] and was measured for magnetic fields in the configuration [bold B][parallel][ital c] up to 10 T and also with respect to various [Theta] angles between the [ital c] axis and field direction. The decrease of [ital j][sub [ital c]] with increasing [ital B] was found to be significantly reduced in comparison to single crystalsmore » and prior results on thin films. A further enhancement in the [ital j][sub [ital c]]([ital B],[ital T]) behavior could not be achieved by chemical doping through partial substitution of copper by zinc.« less