Oscillatory dynamics of a superconductor vortex lattice in high amplitude ac magnetic fields

Abstract

In this work we study by ac susceptibility measurements the evolution of the solid vortex lattice mobility under oscillating forces. Previous work had already shown that in YBCO single crystals, below the melting transition, a temporarily symmetric magnetic ac field (e.g. sinusoidal, square, triangular) can heal the vortex lattice (VL) and increase its mobility, but a temporarily asymmetric one (e.g. sawtooth) of the same amplitude can tear the lattice into a more pinned disordered state. In this work we present evidence that the mobility of the VL is reduced for large vortex displacements, in agreement with predictions of recent simulations. We show that with large symmetric oscillating fields both an initially ordered or an initially disordered VL configuration evolve towards a less mobile lattice, supporting the scenario of plastic flow.

Superconducting vortex pinning with artificial magnetic nanostructures

“…Moreover, this effect may be enhanced by the presence of different resonant frequencies for different vortices in the lattice, depending upon their position with respect to the pinning array. An ideal technique to perform this experiment, in addition to AC magnetotransport, is frequency-dependent AC susceptibility [193].…”

Memory effects and peak effect in type II superconductors

“…sawtooth) becomes less mobile [5]. Moreover, mobility is also reduced if a temporarily symmetric AC field forces vortices into large excursions [9]. Probably, the repeated interactions between neighbors facilitates the healing of topological defects, while temporarily asymmetric AC fields or large vortex excursions promote their creation [10,11].…”

Peak effect in YBCO crystals: statics and dynamics of the vortex lattice

“…In ac susceptibility experiments, the PE is observed as an anomalous increase in shielding capability or a decrease in losses, also usually interpreted as an anomalous decrease in VL mobility. Recent experiments in YBCO crystals, have shown that the mobility of the VL increases after assisting the system with a symmetric ac field (or current) [31] of moderate amplitude [34]. On the other hand, when vortices are assisted by an asymmetric ac field, the VL becomes less mobile [31].…”

“…Recent experiments in YBCO crystals, have shown that the mobility of the VL increases after assisting the system with a symmetric ac …eld (or current) 30 of moderate amplitude 31 . On the other hand, when vortices are assisted by an asymmetric ac …eld, the VL becomes less mobile 30 .…”