Dynamic transition in current-driven disordered flux-line lattice in single-crystal of Bi-2212

We have measured the current-voltage characteristics for both as-grown and irradiated Bi2Sr2CaCu2O8+δ single crystals at T = 5 K in a magnetic field applied parallel to c axis. The results show a variety of dynamical behavior above the depinning threshold, depending on the vortex-vortex interaction (λab/a0) strength and the nature of the quenched disorder (point-like or columnar defects). When the flux lattice is soft, our experimental measurements in both samples have been attributed to plastic flow, including strong metastability and history dependence of the depinning process. The vortex motion in this regime is thought of relatively weakly pinned vortices past more strongly pinned neighbors. A power-law scaling, fit between voltage and applied current can be obtained for the onset of motion in both samples, with different apparent critical exponent depending on defect nature and the strength of interactions. In the plastic regime, the usual scaling ansatz associated with dynamic critical phenomena V scales as (I − Ic)β, where β ∼ 2.2 ± 0.1 and 1.22 ± 0.021 for as-grown and β ≈ 1.49 ± 0.07 for irradiated samples, respectively. Finally, in both cases of defects, with increasing the strength of vortex-vortex interaction a dynamical transition is observed as confirmed by the discontinuity in the vortex-vortex interactions dependence of the critical exponent β. More, our results confirm the important role of the system dimensionnality on vortex dynamics.