Abstract
We study the critical dynamics of vortices associated with dynamic disordering near the depinning transitions driven by dc force (dc current I) and vortex density (magnetic field B). Independent of the driving parameters, I and B, we observe the critical behavior of the depinning transitions, not only on the moving side, but also on the pinned side of the transition, which is the first convincing verification of the theoretical prediction. Relaxation times, tau (I) and tau (B), to reach either the moving or pinned state, plotted against I and B, respectively, exhibit a power-law divergence at the depinning thresholds. The critical exponents of both transitions are, within errors, identical to each other, which are in agreement with the values expected for an absorbing phase transition in the two-dimensional directed-percolation universality class. With an increase in B under constant I, the depinning transition at low B is replaced by the repinning transition at high B in the peak-effect regime. We find a trend that the critical exponents in the peak-effect regime are slightly smaller than those in the low-B regime and the theoretical one, which is attributed to the slight difference in the depinning mechanism in the peak-effect regime.
Highlights
IntroductionWe study the critical dynamics of vortices associated with dynamic disordering near the depinning transitions driven by dc force (dc current I) and vortex density (magnetic field B)
We study the critical dynamics of vortices associated with dynamic disordering near the depinning transitions driven by dc force and vortex density
We find that τ (B) obtained under the particular current Id,p shows a power-law divergence at Bp, indicating that the critical behavior in the moving phase stays unchanged even when the pinned phase shrinks to a point at Bp
Summary
We study the critical dynamics of vortices associated with dynamic disordering near the depinning transitions driven by dc force (dc current I) and vortex density (magnetic field B). The relaxation time τ (I) for the system to settle into the moving steady state (V ∞ > 0 ) exhibits a power-law divergence at the depinning current Id with critical exponents ν = 1.4 ± 0.49,12,20, within error bars, in agreement with the value expected for an absorbing phase transition in the two-dimensional (2D) directed-percolation (DP) universality c lass[36,37,38]. The critical behavior of the depinning transition has been observed only on the moving (fluctuating diffusing [active]) side of the transition[9,12,20,39], that of RIT has been reported on both sides of the transition[20,24,26] This is because it is difficult to obtain a reliable data of V(t) in the pinned (non-fluctuating quiescent [absorbing]) phase, where V(t) relaxes to V ∞ = 0. Critical exponents of the 2D superconductor-insulator transition (SIT) are markedly different depending on whether the SIT is driven by decreasing the film thickness (increasing the normal state resistance) or increasing the magnetic field B43
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