Filamentary flow of vortices with infinite tilt modulus in Bi_2Sr_2Ca_1Cu_2O_{8+δ} single crystal

Abstract

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 Bi_2Sr_2Ca_1Cu_2O_{8+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 <= μ_0H <= 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 μ_0H-Ic curve is due to a metastable state which can be removed after current cycling. At low field, I-V curves exhibit steps which clearly enligth a "fingerprint phenomenon" as it can be seen the current dependence of the differential resistance Rd = dV/dI. We associate this to vortices flow through uncorrelated channels for the highly defective lattice. Indeed, as field sufficiently increase, these peaks merge giving 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 βdetermined in the vicinity of the threshold current using the power-law scaling V (I-Ic)^βwith 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 which confirms the pseudo-2D behaviour of the FLL. Our transport studies are in good agreement with recent simulations results of 2D elastic objects driven by repulsive interactions through a random pinning potential.