Moving vortex matter with coexisting vortices and anti-vortices

TL;DR

This paper presents a theoretical model for vortex and anti-vortex dynamics in thin superconducting films with nanostructured defects, revealing multiple steady states with coexisting vortices and anti-vortices driven by transport currents.

Contribution

A simple London model incorporating vortex anti-vortex pair creation and annihilation dynamics in superconducting films with nanostructures is proposed.

Findings

Multiple steady states with coexisting vortices and anti-vortices are possible.

Vortex anti-vortex pairs can be created by small transport currents near defects.

The model explains vortex matter behavior at zero magnetic field and low temperatures.

Abstract

Moving vortex matter, driven by transport currents independent of time, in which vortices and anti-vortices coexist is investigated theoretically in thin superconducting films with nanostructured defects. A simple London model is proposed for the vortex dynamics in films with periodic arrays of nanomagnets or cylindrical holes (antidots). Common to these films is that vortex anti-vortex pairs may be created in the vicinity of the defects by relatively small transport currents, because it adds to the current generated by the defects - the nanomagnets screening current, or the antidots backflow current - and may exceed locally the critical value for vortex anti-vortex pair creation. The model assumes that vortex matter dynamics is governed by Langevin equations, modified to account for creation and annihilation of vortex anti-vortex pairs. For pair creation, it is assumed that whenever the total current at some location exceeds a critical value, equal to that needed to separate a vortex from an anti-vortex by a vortex core diameter, a pair is created instantaneously around this location. Pair annihilation occurs by vortex anti-vortex collisions. The model is applied to films at zero external magnetic field and low temperatures. It is found that several moving vortex matter steady-states with equal numbers of vortices and anti-vortices are possible.