Current - voltage characteristics of multifilamentary tapes in zero applied magnetic field

Current - voltage characteristics of multifilamentary tapes (short samples) produced by the `powder in tube' technique were measured at different temperatures close to the mean-field critical temperature, and in zero applied magnetic field. After performing the required corrections due to the current flowing in the silver matrix, the I - V curves were interpreted in terms of current-induced unbinding of the thermally created vortex - antivortex pairs. Two possible mechanisms for appearance of a finite critical current in zero applied magnetic field are discussed: the Jensen - Minnhagen quasi-two-dimensional (2D) approach, that takes into account the interlayer Josephson coupling, and a model of size limitation of vortex fluctuations. From our analysis, it seems that the latter model is more suitable for this kind of superconducting material, due probably to an accentuated intrinsic anisotropy.