Irreversible flow of vortex matter: polycrystal and amorphous phases

TL;DR

This paper explores how the topology of vortex matter influences its flow behavior, distinguishing between polycrystalline and amorphous phases, and analyzing their depinning mechanisms and steady state dynamics.

Contribution

It provides a detailed comparison of vortex flow in polycrystalline and amorphous phases, highlighting the topological effects on depinning and flow patterns.

Findings

Polycrystalline vortex lattices exhibit filamentary flow due to dislocation dynamics.

Amorphous vortex matter shows channel-like flow and no lattice order.

Critical current scales with impurity density and differs between phases.

Abstract

We investigate the microscopic mechanisms giving rise to plastic depinning and irreversible flow in vortex matter. The topology of the vortex array crucially determines the flow response of this system. To illustrate this claim, two limiting cases are considered: weak and strong pinning interactions. In the first case disorder is strong enough to introduce plastic effects in the vortex lattice. Diffraction patterns unveil polycrystalline lattice topology with dislocations and grain boundaries determining the electromagnetic response of the system. Filamentary flow is found to arise as a consequence of dislocation dynamics. We analize the stability of vortex lattices against the formation of grain boundaries, as well as the steady state dynamics for currents approaching the depinning critical current from above, when vortex motion is mainly localized at the grain boundaries. On the contrary, a dislocation description proves no longer adequate in the second limiting case examined. For strong pinning interactions, the vortex array appears completely amorphous and no remnant of the Abrikosov lattice order is left. Here we obtain the critical current as a function of impurity density, its scaling properties, and characterize the steady state dynamics above depinning. The plastic depinning observed in the amorphous phase is tightly connected with the emergence of channel-like flow. Our results suggest the possibility of establishing a clear distinction between two topologically disordered vortex phases: the vortex polycrystal and the amorphous vortex matter.