Current-voltage characteristics in a superconducting Bi-2223 tape in the range of very low electric field

Current-voltage characteristics in the range of very low electric field were analyzed from a relaxation of the magnetization using a SQUID magnetometer in a superconducting Bi-2223 tape. It was found that the observed current-voltage characteristics in this range were scaled well as predicted by the vortex glass-liquid transition theory. However, the obtained transition field was much lower than that obtained from a scaling in the higher electric field range. At the same time, the dynamic critical index, z, was much larger than usual values. Hence, it is concluded that these parameters are not uniquely determined independently of the level of electric field. The experimental result was compared with the theoretical analysis using the flux creep-flow theory in which the distribution of the effective flux pinning strength was taken into account. It was found that the theoretical result explains approximately the observed result. This shows that the essential mechanism which governs the transport property in the superconducting tape is the flux pinning