1,091 research outputs found
Collective transport in the insulating state of Josephson junction arrays
We investigate collective Cooper-pair transport of one- and two-dimensional
Josephson junction arrays in the insulating state. We derive an analytical
expression for the current-voltage characteristic revealing thermally activated
conductivity at small voltages and threshold voltage depinning. The activation
energy and the related depinning voltage represent a dynamic Coulomb barrier
for collective charge transfer over the whole system and scale with the system
size. We show that both quantities are non-monotonic functions of magnetic
field. We propose that formation of the dynamic Coulomb barrier as well as the
size scaling of the activation energy and the depinning threshold voltage, are
consequences of the mutual phase synchronization. We apply the results for
interpretation of experimental data in disordered films near the
superconductor-insulator transition.Comment: 4 pages, 2 figures; typos corrected, new figures, an improved fit to
experimental dat
Driven depinning of strongly disordered media and anisotropic mean-field limits
Extended systems driven through strong disorder are modeled generically using
coarse-grained degrees of freedom that interact elastically in the directions
parallel to the driving force and that slip along at least one of the
directions transverse to the motion. A realization of such a model is a
collection of elastic channels with transverse viscous couplings. In the
infinite range limit this model has a tricritical point separating a region
where the depinning is continuous, in the universality class of elastic
depinning, from a region where depinning is hysteretic. Many of the collective
transport models discussed in the literature are special cases of the generic
model.Comment: 4 pages, 2 figure
Irreversible flow of vortex matter: polycrystal and amorphous phases
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.Comment: 13 pages, 16 figure
Collective Coordinates Theory for Discrete Soliton Ratchets in the sine-Gordon Model
A collective coordinate theory is develop for soliton ratchets in the damped
discrete sine-Gordon model driven by a biharmonic force. An ansatz with two
collective coordinates, namely the center and the width of the soliton, is
assumed as an approximated solution of the discrete non-linear equation. The
evolution of these two collective coordinates, obtained by means of the
Generalized Travelling Wave Method, explains the mechanism underlying the
soliton ratchet and captures qualitatively all the main features of this
phenomenon. The theory accounts for the existence of a non-zero depinning
threshold, the non-sinusoidal behaviour of the average velocity as a function
of the difference phase between the harmonics of the driver, the non-monotonic
dependence of the average velocity on the damping and the existence of
non-transporting regimes beyond the depinning threshold. In particular it
provides a good description of the intriguing and complex pattern of subspaces
corresponding to different dynamical regimes in parameter space
Collective Sliding States for Colloidal Molecular Crystals
We study the driving of colloidal molecular crystals over periodic substrates
such as those created with optical traps. The n-merization that occurs in the
colloidal molecular crystal states produces a remarkably rich variety of
distinct dynamical behaviors, including polarization effects within the pinned
phase and the formation of both ordered and disordered sliding phases. Using
computer simulations, we map the dynamic phase diagrams as a function of
substrate strength for dimers and trimers on a triangular substrate, and
correlate features on the phase diagram with transport signatures.Comment: 4 pages, 5 postscript figure
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