Reversible to Irreversible Flow Transition in Periodically Driven Vortices

We show that periodically driven superconducting vortices in the presence of quenched disorder exhibit a transition from reversible to irreversible flow under increasing vortex density or cycle period. This type of behavior has recently been observed for periodically sheared colloidal suspensions and we demonstrate that driven vortex systems exhibit remarkably similar behavior. We also provide evidence that the onset of irreversible behavior is a dynamical phase transition.Comment: 4 pages, 4 postscript figures. Version to appear in Physical Review Letter

Local Melting and Drag for a Particle Driven Through a Colloidal Crystal

We numerically investigate a colloidal particle driven through a colloidal crystal as a function of temperature. When the charge of the driven particle is larger or comparable to that of the colloids comprising the crystal, a local melting can occur, characterized by defect generation in the lattice surrounding the driven particle. The generation of the defects is accompanied by an increase in the drag force on the driven particle, as well as large noise fluctuations. We discuss the similarities of these results to the peak effect phenomena observed for vortices in superconductors.Comment: 4 pages, 4 postscript figure

Pinning and Dynamics of Colloids on One Dimensional Periodic Potentials

Using numerical simulations we study the pinning and dynamics of interacting colloids on periodic one-dimensional substrates. As a function of colloid density, temperature, and substrate strength, we find a variety of pinned and dynamic states including pinned smectic, pinned buckled, two-phase flow, and moving partially ordered structures. We show that for increasing colloid density, peaks in the depinning threshold occur at commensurate states. The scaling of the pinning threshold versus substrate strength changes when the colloids undergo a transition from one-dimensional chains to a buckled configuration.Comment: 4 pages, 4 postscript figure

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

Charge Transport Transitions and Scaling in Disordered Arrays of Metallic Dots

We examine the charge transport through disordered arrays of metallic dots using numerical simulations. We find power law scaling in the current-voltage curves for arrays containing no voids, while for void-filled arrays charge bottlenecks form and a single scaling is absent, in agreement with recent experiments. In the void-free case we also show that the scaling exponent depends on the effective dimensionality of the system. For increasing applied drives we find a transition from 2D disordered filamentary flow near threshold to a 1D smectic flow which can be identified experimentally using characteristics in the transport curves and conduction noise.Comment: 4 pages, 4 postscript figure

Fibrillar templates and soft phases in systems with short-range dipolar and long-range interactions

We analyze the thermal fluctuations of particles that have a short-range dipolar attraction and a long-range repulsion. In an inhomogeneous particle density region, or "soft phase," filamentary patterns appear which are destroyed only at very high temperatures. The filaments act as a fluctuating template for correlated percolation in which low-energy excitations can move through the stable pattern by local rearrangements. At intermediate temperatures, dynamically averaged checkerboard states appear. We discuss possible implications for cuprate superconducting and related materials.Comment: 4 pages, 4 postscript figures. Discussion of implications for experiment and theory has been expande

Transient Pattern Formation in an Active Matter Contact Poisoning Model

One of the most notable features in repulsive particle based active matter systems is motility-induced-phase separation (MIPS) where a dense, often crystalline phase coexists with a low density fluid. In most active matter studies, the activity is kept constant as a function of time; however, there are many examples of active systems in which individual particles transition from living or moving to dead or nonmotile due to lack of fuel, infection, or poisoning. Here we consider an active matter particle system at densities where MIPS does not occur. When we add a small number of infected particles that can effectively poison other particles, rendering them nonmotile, we find a rich variety of time dependent pattern formation, including MIPS, a wetting phase, and a fragmented state formed when mobile particles plow through an nonmotile packing. We map out the patterns as a function of time scaled by the duration of the epidemic, and show that the pattern formation is robust for a wide range of poisoning rates and activity levels. We also show that pattern formation does not occur in a random death model, but requires the promotion of nucleation by contact poisoning. Our results should be relevant to biological and active matter systems where there is some form of poisoning, death, or transition to nonmotility.Comment: 7 pages, 6 figure

Static and dynamic friction in sliding colloidal monolayers

In a pioneer experiment, Bohlein et al. realized the controlled sliding of two-dimensional colloidal crystals over laser-generated periodic or quasi-periodic potentials. Here we present realistic simulations and arguments which besides reproducing the main experimentally observed features, give a first theoretical demonstration of the potential impact of colloid sliding in nanotribology. The free motion of solitons and antisolitons in the sliding of hard incommensurate crystals is contrasted with the soliton-antisoliton pair nucleation at the large static friction threshold Fs when the two lattices are commensurate and pinned. The frictional work directly extracted from particles' velocities can be analysed as a function of classic tribological parameters, including speed, spacing and amplitude of the periodic potential (representing respectively the mismatch of the sliding interface, and the corrugation, or "load"). These and other features suggestive of further experiments and insights promote colloid sliding to a novel friction study instrument.Comment: in print in the Proceedings of the National Academy of Sciences U.S.A. This v2 is identical to v1, but includes ancillary material. A few figures were undersampled due to size limits: those in v1 are far sharpe