Dynamic instabilities and memory effects in vortex matter

TL;DR

This paper investigates complex vortex dynamics in superconductors, revealing memory effects and instabilities, and proposes a model based on competition between vortex disorder injection and annealing, supported by experimental data.

Contribution

It introduces a generic mechanism explaining vortex memory effects and instabilities, supported by experimental validation in NbSe2 crystals.

Findings

Memory effects are linked to spatial variation of vortex disorder.

Surface barriers influence vortex phase injection and annealing.

Experimental data confirms the proposed model.

Abstract

Recent studies have shown a number of surprising vortex dynamics phenomena both in low and high temperature superconductors, which include: low frequency noise, slow voltage oscillations, history dependent dynamic response, memory of the direction, amplitude, duration, and frequency of the previously applied current, suppression of a large ac vortex response by a very small dc bias, and a strong frequency dependence. Taken together, these phenomena are incompatible with the current understanding of bulk vortex dynamics. We propose a generic mechanism to account for these observations in terms of the competition between the injection of a disordered vortex phase through the surface barriers at the sample edges, and the annealing of this metastable disorder by the transport current. The model is confirmed by investigating the current distribution across NbSe2 single crystals using arrays of Hall sensors. For an ac current only narrow regions near the edges are in the pinned disordered phase resulting in a large response. In the presence of a dc bias a wide region of the sample is filled by the disordered phase preventing vortex motion. The resulting spatial variation of the disorder across the sample acts as an active memory of the previously applied current sequence.