I-V curves of BSCCO tape carrying DC current exposed to perpendicular and parallel AC fields

A study of the DC I-V curves of BSCCO tapes exposed to AC perpendicular and parallel magnetic fields is presented. AC magnetic fields with amplitudes up to 700 G and frequencies from 1 to 430 Hz have been applied perpendicular and parallel to tapes carrying DC currents at T=77 K. Both field orientations result in a significant DC electric field increase, in comparison to applying DC magnetic fields of the same intensity. However, the observed I-V curves behavior is different for the perpendicular and parallel cases. In the perpendicular case, we distinguish between two frequency regimes: for frequencies above 40 Hz, the observed I-V curves obey the empirical power law dependence with current density, J_C, and power index, n, that strongly depend on the field amplitude. For frequencies below 20 Hz, the observed I-V curves deviate from power law description. In the parallel field case, the I-V curve can be regarded as a superposition of an additional DC voltage over the no field I-V curve. This additional voltage increases with increasing current, peaks near the critical current and decreases thereafter. The results are discussed assuming a narrowing down of the DC current path under the application of a perpendicular AC field. Shaking of the pinned vortices under the application of a parallel AC field is assumed for explaining the results in this case.