Local studies of vortex instabilities and memory effects in NbSe2

Recent studies have shown a number of surprising vortex dynamics phenomena which include: low frequency noise, slow voltage oscillations, history depe ndent dynamic response, memory of the direction, amplitude, and frequency o f the previously applied current, suppression of the ac response by a small de bias, and a strong frequency dependence. These phenomena are incompatib le with the current understanding of bulk vortex dynamics. We propose a gen eric mechanism in terms of the competition between the injection of a disor dered vortex phase through the surface barriers, and the annealing of this metastable disorder by the transport current. The model is confirmed by inv estigating the current distribution across 2H-NbSe2 crystals using arrays o f Hall sensors.