Effect of Vortex Annihilation Lines on Current-Voltage Characteristics of High-T Superconducting Wires

Recently, a new theoretical model has demonstrated the important contribution vortex annihilation lines may have to the flux dynamics in superconductors. The local divergence in the current density, where vortices of different polarities annihilate each other, redistributes the current density over the superconductor cross-section and leads to a slowdown of the dynamics in the presence of zero-field lines in the sample. In this work we extend the theory and explore experimentally the current-voltage curves of BSCCO tapes carrying transport currents and exposed to external magnetic fields. While the transport current naturally creates a zero-field line in the center of the tape, the external field shifts the position of this line and may eliminate the line altogether, depending on the levels of both, current and field. By varying these conditions, we show, both theoretically and experimentally, that the current-voltage curves change with the crossover from presence to absence of an annihilation line in the sample, supporting the slowdown of dynamics in the presence of this line. With the growing demand for and use of superconducting wires and tapes, these results may play an important role when using the tapes in practical applications. Specifically, operating conditions where an annihilation line is present would be favorable.