Transition from thermally activated to regular flow of magnetic flux vortices in HTSC

The effect of structural inhomogeneities in a superconductor on a vortex me dium flow in weak magnetic fields at temperatures varying from 78 to 83 K f or various bias current densities is investigated by using transport measur ements of Bi2Sr2CaCu2O8+x thin-film microbridges. The results obtained are analyzed on the basis of the theories of flux creep and the regular flow of vortices. It is shown that the current dependences of the effective potent ial for vortex pinning can be satisfactorily described in the framework of two statistical models, one of which was proposed earlier by the authors. B oth models cover the regimes of thermally activated and regular flow of vor tices as limiting cases. The wide transition region in which the creep and regular vortex flow processes simultaneously occur due to a large dispersio n in the pinning energy distribution. It is found that when the magnetic fi eld exceeds a certain value, the average value and dispersion of the pinnin g potential decrease sharply, so that the conditions of regular flow set in even for small values of the bias current. This fact is attributed to the destruction of vortex lines into two-dimensional segments. (C) 2000 MAIK "N auka/ Interperiodica".