arXiv subjects

C. Reichhardt

Publications and source records attributed to C. Reichhardt.

At least 271 records · Page 15Linked to original sources

arXiv2003

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.

cond-mat.mes-hall↗

arXiv2003

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.

cond-mat.soft↗

arXiv2003

Structure and Melting of Two-Species Charged Clusters in a Parabolic Trap

We consider a system of charged particles interacting with an unscreened Coulomb repulsion in a two-dimensional parabolic confining trap. The static charge on a portion of the particles is twice as large as the charge on the remaining particles. The particles separate into a shell structure with those of greater charge situated farther from the center of the trap. As we vary the ratio of the number of particles of the two species, we find that for certain configurations, the symmetry of the arrangement of the inner cluster of singly-charged particles matches the symmetry of the outer ring of doubly-charged particles. These matching configurations have a higher melting temperature and a higher thermal threshold for intershell rotation between the species than the nonmatching configurations.

cond-mat.soft↗

arXiv2003

Glassy Ratchets for Collectively Interacting Particles

We show that ratchet effects can occur in a glassy media of interacting particles where there is no quenched substrate. We consider simulations of a disordered binary assembly of colloids in which only one species responds to a drive. We apply an asymmetric ac drive that would produce no net dc drift of an isolated overdamped particle. When interacting particles are present, the asymmetric ac drive produces a ratchet effect. A simple model captures many of the results from simulations, including flux reversals as a function of density and temperature.

cond-mat.soft↗

arXiv2003

Absolute Transverse Mobility and Ratchet Effect on Periodic 2D Symmetric Substrates

We present a simple model of an overdamped particle moving on a two dimensional symmetric periodic substrate with a dc drive in the longitudinal direction and additional ac drives in both the longitudinal and transverse directions. For certain regimes we find that a finite longitudinal dc force produces a net dc response only in the transverse direction, which we term absolute transverse mobility. Additionally we find regimes exhibiting a ratchet effect in the absence of an applied dc drive.

cond-mat.stat-mech↗

arXiv2003

Superconducting Vortex Logic Antidots

We examine a building block for logic devices in which the positions of superconducting vortices in coupled elongated antidots provide the elementary logic states of 0 and 1. We show analytically and through simulation the maximum operating frequency of a pair of antidots as a function of antidot spacing and elongation. At finite temperatures, a signal can propagate through a series of identically shaped antidots with correctly chosen spacing, with an exponential distribution of switching times for the signal to move over by one antidot.

cond-mat.supr-con↗

arXiv2003

Temperature and ac Effects on Charge Transport in Metallic Arrays of Dots

We investigate the effects of finite temperature, dc pulse, and ac drives on the charge transport in metallic arrays using numerical simulations. For finite temperatures there is a finite conduction threshold which decreases linearly with temperature. Additionally we find a quadratic scaling of the current-voltage curves which is independent of temperature for finite thresholds. These results are in excellent agreement with recent experiments on 2D metallic dot arrays. We have also investigated the effects of an ac drive as well as a suddenly applied dc drive. With an ac drive the conduction threshold decreases for fixed frequency and increasing amplitude and saturates for fixed amplitude and increasing frequency. For sudden applied dc drives below threshold we observe a long time power law conduction decay.

cond-mat.mes-hall↗

arXiv2003

Metastability and Transient Effects in Vortex Matter Near a Decoupling Transition

We examine metastable and transient effects both above and below the first-order decoupling line in a 3D simulation of magnetically interacting pancake vortices. We observe pronounced transient and history effects as well as supercooling and superheating between the 3D coupled, ordered and 2D decoupled, disordered phases. In the disordered supercooled state as a function of DC driving, reordering occurs through the formation of growing moving channels of the ordered phase. No channels form in the superheated region; instead the ordered state is homogeneously destroyed. When a sequence of current pulses is applied we observe memory effects. We find a ramp rate dependence of the V(I) curves on both sides of the decoupling transition. The critical current that we obtain depends on how the system is prepared.

cond-mat.supr-con↗

arXiv2003

Simulations of Noise in Disordered Systems

We use particle dynamics simulations to probe the correlations between noise and dynamics in a variety of disordered systems, including superconducting vortices, 2D electron liquid crystals, colloids, domain walls, and granular media. The noise measurements offer an experimentally accessible link to the microscopic dynamics, such as plastic versus elastic flow during transport, and can provide a signature of dynamical reordering transitions in the system. We consider broad and narrow band noise in transport systems, as well as the fluctuations of dislocation density in a system near the melting transition.

cond-mat.supr-con↗

arXiv2003

Dynamics and Melting of Stripes, Crystals, and Bubbles with Quenched Disorder

Two-dimensional systems in which there is a competition between long-range repulsion and short range attraction exhibit a remarkable variety of patterns such as stripes, bubbles, and labyrinths. Such systems include magnetic films, Langmuir monolayers, polymers, gels, water-oil mixtures, and two-dimensional electron systems. In many of these systems quenched disorder from the underlying substrate may be present. We examine the dynamics and stripe formation in the presence of both an applied dc drive and quenched disorder. When the disorder strength exceeds a critical value, an applied dc drive can induce a dynamical stripe ordering transition to a state that is more ordered than the originating undriven, unpinned pattern.

cond-mat.soft↗

arXiv2002

Effect of FET geometry on charge ordering of transition metal oxides

We examine the effect of an FET geometry on the charge ordering phase diagram of transition metal oxides using numerical simulations of a semiclassical model including long-range Coulomb fields, resulting in nanoscale pattern formation. We find that the phase diagram is unchanged for insulating layers thicker than approximately twice the magnetic correlation length. For very thin insulating layers, the onset of a charge clump phase is shifted to lower values of the strength of the magnetic dipolar interaction, and intermediate diagonal stripe and geometric phases can be suppressed. Our results indicate that, for sufficiently thick insulating layers, charge injection in an FET geometry can be used to experimentally probe the intrinsic charge ordering phases in these materials.

cond-mat.mes-hall↗

arXiv2002

Ratchet Cellular Automata

In this work we propose a ratchet effect which provides a general means of performing clocked logic operations on discrete particles, such as single electrons or vortices. The states are propagated through the device by the use of an applied AC drive. We numerically demonstrate that a complete logic architecture is realizable using this ratchet. We consider specific nanostructured superconducting geometries using superconducting materials under an applied magnetic field, with the positions of the individual vortices in samples acting as the logic states. These devices can be used as the building blocks for an alternative microelectronic architecture.

cond-mat.stat-mech↗

arXiv2002

Frustration and Melting of Colloidal Molecular Crystals

Using numerical simulations we show that a variety of novel colloidal crystalline states and multi-step melting phenomena occur on square and triangular two-dimensional periodic substrates. At half-integer fillings different kinds of frustration effects can be realized. A two-step melting transition can occur in which individual colloidal molecules initially rotate, destroying the overall orientational order, followed by the onset of interwell colloidal hopping, in good agreement with recent experiments.

cond-mat.soft↗

arXiv2002

Depinning by Fracture in a Glassy Background

We force a single particle through a two-dimensional simulated glass. We find that the particle velocity obeys a robust power law that persists to drives well above threshold. As the single driven particle moves, it induces cooperative distortions in the surrounding medium. We show theoretically that a fracture model for these distortions produces power law behavior, and discuss implications for experimental probes of soft matter systems.

cond-mat.soft↗

arXiv2002

Fluctuating Topological Defects in 2D Liquids: Heterogeneous Motion and Noise

We measure the defect density as a function of time at different temperatures in simulations of a two dimensional system of interacting particles. Just above the solid to liquid transition temperature, the power spectrum of the defect fluctuations shows a 1/f signature, which crosses over to a white noise signature at higher temperatures. When 1/f noise is present, the 5-7 defects predominately form string like structures, and the particle trajectories show a 1D correlated motion that follows the defect strings. At higher temperatures this heterogeneous motion is lost. We demonstrate this heterogeneity both in systems interacting with a short ranged screened Coulomb interaction, as well as in systems with a long range logarithmic interaction between the particles.

cond-mat.soft↗

arXiv2002

Dynamical Ordering of Driven Stripe Phases in Quenched Disorder

We examine the dynamics and stripe formation in a system with competing short and long range interactions in the presence of both an applied dc drive and quenched disorder. Without disorder, the system forms stripes organized in a labyrinth state. We find that, when the disorder strength exceeds a critical value, an applied dc drive can induce a dynamical stripe ordering transition to a state that is more ordered than the originating undriven, unpinned pattern. We show that signatures in the structure factor and transport properties correspond to this dynamical reordering transition, and we present the dynamic phase diagram as a function of strengths of disorder and dc drive.

cond-mat.soft↗

arXiv2002

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.

cond-mat.mes-hall↗

arXiv2002

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.

cond-mat.supr-con↗