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 dependent dynamic response, memory of the direction, amplitude, and frequency of the previously applied current, suppression of the ac response by a small de bias, and a strong frequency dependence. These phenomena are incompatible with the current understanding of bulk vortex dynamics. We propose a generic mechanism in terms of the competition between the injection of a disordered vortex phase through the surface barriers, and the annealing of this metastable disorder by the transport current. The model is confirmed by investigating the current distribution across 2H-NbSe2 crystals using arrays of Hall sensors.