Depinning of a metastable disordered vortex lattice

The experiments presented, provides information on the depinning process of a strongly pinned vortex lattices. It is found that depinning is governed by current driven vortex rearrangements leading to the formation of regions with weakly pinned vortices. These vortex rearrangements occur without a measurable voltage response, which appears only upon the creation of a channel of mobile vortices connecting the sample edges. The creation time of such channels gives rise to the observed delays in voltage response to subcritical driving currents as well as to the ramping rate dependence of the critical currents.