Irreversible flow of vortex matter: Polycrystal and amorphous 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 disorder forces. 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 analyze 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 disorder forces, 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.

Memory formation and evolution of the vortex configuration associated with random organization

“…The RIT may also be interpreted as a kind of a plastic depinning transition where irreversible vortex motion occurs in correspondence with the flow of topological defects in the lattice [40,41]. Concerning dynamic ordering under ac and dc driving forces, Valenzuela reported a numerical study that simultaneously addresses the order and mobility of the vortex lattice [42].…”

Nonequilibrium depinning transition of ac driven vortices with random pinning

“…Previous experimental and numerical studies on the nonequilibrium depinning transition have focused only on the response to the dc drive, while it is well known for the vortex system that the ac external forces, namely, the ac current I ac and the ac magnetic field, are readily used to depin and order the vortex lattice [9,13,24,25,[30][31][32][33]. For the ac current-voltage (| |-| | I V ac ac ) characteristics, an increase in the frequency f as well as the amplitude | | I ac of the ac drive I ac causes an enhancement of the amplitude | | V ac of the ac voltage.…”

Competition between dynamic ordering and disordering for vortices driven by superimposed ac and dc forces

“…The increase of | ( )| V t with t observed during the readout process is indicative of random organization [4]. After being subjected to the ac drive with d=2 μm for many cycles, the final vortex configuration becomes organized compared to the initial one [54][55][56][57]. This change is drawn schematically by lighter blue in the right diagram than in the lower left one of figure 2.…”