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We study the general phenomenon of plastic depinning using a vortex system confined in a Corbino-disc superconductor. For an ordered initial vortex configuration, the vortices driven by a suddenly applied dc current (force) are gradually pinned to random pinning centers, indicating dynamic disordering. This is detected from the decaying of voltage V (t) (mean velocity) toward a steady-state value V ∞ . On the other hand, when the initial configuration is disordered, a gradual increase of V (t) toward V ∞ is observed, reflecting dynamic ordering. In both cases, relaxation times to reach the steady state exhibit a power-law divergence at the depinning current. Our results clearly show that the transient response depends on the initial vortex configurations: however, the transient time as well as the final mean vortex velocity only depends on the applied current, and the critical behaviors of the depinning transition are identical. To the best of our knowledge, this work is the first to demonstrate this fact predicted by numerical simulations and other more indirect experiments (e.g. Pérez Daroca et al 2011 Phys. Rev. B 84 012508).

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We measure current-voltage (I-V) characteristics in a weakly disordered vortex-lattice phase of an amorphous Mo x Ge 1−x film at various temperatures T down to near T = 0 and perform a scaling analysis using recent simulations for a plastic depinning transition where a continuous velocity-force response is predicted. The collapse of the I-V data onto a scaling function is observed, whereas critical exponents derived via the scaling analysis are larger than the predicted ones. This discrepancy is partially attributed to the unexpectedly weak T dependence of the I-V characteristics at low T.