Filamentary flow of vortices in a Bi2Sr2Ca1Cu2O8+δ single crystal

Using micro-bridge technique, we have studied the vortex dynamics in a very low temperature region (i.e. T/TC → 0) of the B-T phase diagram of Bi2Sr2Ca1Cu2O8+δ single crystal. We distinguish two types of vortex dynamics near the depinning threshold depending on the magnitude of the vortex-vortex interactions. For 0.01≤μ0H<1T, we show that current-voltage characteristics (I-V) are strongly dependent on the history of magnetic field and current cycling. The sharp peak, so called “peak effect” (PE), observed in μ0H-Ic curve is due to a metastable state that can be removed after current cycling. At low field, I-V curves show steps that would be clearly related to “fingerprint phenomenon” since the relationship Rd = dV/dI exists. This can be attributed to vortices flow through uncorrelated channels for the highly defective lattice. Indeed, as field sufficiently increases, these peaks merge to make broader ones indicating a crossover from filamentaty strings to braid river like in which vortex-vortex interactions becomes significant. As confirmed by the discontinuity in the critical exponent value β determined in the vicinity of the threshold current using the power-law scaling V∼(I-Ic) with a crossover from β = 2.2 to β = 1.2. The strong vortex correlation along the c-axis has been clearly demonstrated using the dc-flux-transformer geometry for transport measurements that confirms the pseudo-2D behaviour of the FLL. Our transport studies are in good agreement with simulations results of 2D elastic objects driven by repulsive interactions through a random pinning potential.