21 research outputs found
Vortex lattices in strong type-II superconducting two-dimensional strips
We show how to calculate semi-analytically the dense vortex state in strong
type-II superconducting nanostructures. For the specific case of a strip, we
find vortex lattice solutions which also incorporate surface superconductivity.
We calculate the energy cost to displace individual vortex rows parallel to the
surfaces and find that this energy oscillates with the magnetic field.
Remarkably, we also find that, at a critical field below , this
''shear'' energy becomes strictly zero for the surface rows due to an
unexpected mismatch with the bulk lattice.Comment: Title, abstract, and some text paragraphs have been rewritte
Mode locking of vortex matter driven through mesoscopic channels
We investigated the driven dynamics of vortices confined to mesoscopic flow
channels by means of a dc-rf interference technique. The observed mode-locking
steps in the -curves provide detailed information on how the number of rows
and lattice structure in the channel change with magnetic field. Minima in flow
stress occur when an integer number of rows is moving coherently, while maxima
appear when incoherent motion of mixed and row configurations is
predominant. Simulations show that the enhanced pinning at mismatch originates
from quasi-static fault zones with misoriented edge dislocations induced by
disorder in the channel edges.Comment: some minor changes were made, 4 pages, 4 figures, accepted for
publication in Phys. Rev. Let
Directional vortex motion guided by artificially induced mesoscopic potentials
Rectangular pinning arrays of Ni dots define a potential landscape for vortex
motion in Nb films. Magnetotransport experiments in which two in-plane
orthogonal electrical currents are injected simultaneously allow selecting the
direction and magnitude of the Lorentz force on the vortex-lattice, thus
providing the angular dependence of the vortex motion. The background
dissipation depends on angle at low magnetic fields, which is progressively
smeared out with increasing field. The periodic potential locks in the vortex
motion along channeling directions. Because of this, vortex-lattice direction
of motion is up to 85o away from the applied Lorentz force direction.Comment: PDF file includes figure
Incommensuration Effects and Dynamics in Vortex Chains
We examine the motion of one-dimensional (1D) vortex matter embedded in a 2D
vortex system with weak pinning using numerical simulations. We confirm the
conjecture of Matsuda et al. [Science 294, 2136 (2001)] that the onset of the
temperature induced motion of the chain is due to an incommensuration effect of
the chain with the periodic potential created by the bulk vortices. In
addition, under an applied driving force we find a two stage depinning
transition, where the initial depinning of the vortex chain occurs through
soliton like pulses. When an ac drive is added to the dc drive, we observe
phase locking of the moving vortex chain.Comment: 4 pages, 4 postscript figure
Effect of electron irradiation on vortex dynamics in YBa_2Cu_3O_{7-x} single crystals
We report on drastic change of vortex dynamics with increase of quenched
disorder: for rather weak disorder we found a single vortex creep regime, which
we attribute to a Bragg-glass phase, while for enhanced disorder we found an
increase of both the depinning current and activation energy with magnetic
field, which we attribute to entangled vortex phase. We also found that
introduction of additional defects always increases the depinning current, but
it increases activation energy only for elastic vortex creep, while it
decreases activation energy for plastic vortex creep.Comment: 4 pages, 3 figures, submited to Phys. Rev.
Influence of vortex-vortex interaction on critical currents across low-angle grain boundaries in YBa2Cu3O7-delta thin films
Low-angle grain boundaries with misorientation angles theta < 5 degrees in
optimally doped thin films of YBCO are investigated by magnetooptical imaging.
By using a numerical inversion scheme of Biot-Savart's law the critical current
density across the grain boundary can be determined with a spatial resolution
of about 5 micrometers. Detailed investigation of the spatially resolved flux
density and current density data shows that the current density across the
boundary varies with varying local flux density. Combining the corresponding
flux and current pattern it is found that there exists a universal dependency
of the grain boundary current on the local flux density. A change in the local
flux density means a variation in the flux line-flux line distance. With this
knowledge a model is developped that explains the flux-current relation by
means of magnetic vortex-vortex interaction.Comment: 7 pages, 14 figure
Dynamic ordering and frustration of confined vortex rows studied by mode-locking experiments
The flow properties of confined vortex matter driven through disordered
mesoscopic channels are investigated by mode locking (ML) experiments. The
observed ML effects allow to trace the evolution of both the structure and the
number of confined rows and their match to the channel width as function of
magnetic field. From a detailed analysis of the ML behavior for the case of
3-rows we obtain ({\it i}) the pinning frequency , ({\it ii}) the onset
frequency for ML ( ordering velocity) and ({\it iii}) the
fraction of coherently moving 3-row regions in the channel. The
field dependence of these quantities shows that, at matching, where is
maximum, the pinning strength is small and the ordering velocity is low, while
at mismatch, where is small, both the pinning force and the ordering
velocity are enhanced. Further, we find that , consistent
with the dynamic ordering theory of Koshelev and Vinokur. The microscopic
nature of the flow and the ordering phenomena will also be discussed.Comment: 10 pages, 7 figure, submitted to PRB. Discussion has been improved
and a figure has been adde
Matching and surface barrier effects of the flux-line lattice in superconducting films and multilayers.
The flux-line lattice dissipation and the pinning force of Bi2Sr2CaCu2O8 and YBa2Cu3O7 films and a Nb/Cu multilayer are investigated with the vibrating reed technique. In magnetic fields oriented under a small angle with respect to the film surfaces the Bi-2:2:1:2 film shows a series of pronounced dissipation maxima at matching fields BN in the irreversible region of the magnetic phase diagram. The Y-1:2:3 film shows tiny damping maxima, whereas no structure in the dissipation of the Nb/Cu multilayer is detected below the upper critical field. The comparison of the matching fields to an anisotropic London model shows that the dissipation maxima are caused by rearrangements of the flux-line lattice configuration due to interactions with the sample surface. The different behavior of the high-temperature superconductors and the Nb/Cu multilayer is understood by explicitly taking the surface barrier into account. Deviations from the surface induced commensurability of the flux-line lattice due to the intrinsic pinning are discussed. Our results indicate that pancake vortices in the Bi-2:2:1:2 film should be coupled below the irreversibility line and below magnetic fields B??0.5 T perpendicular to the film surface