arXiv subjects

C. Reichhardt

Publications and source records attributed to C. Reichhardt.

At least 73 records · Page 4Linked to original sources

arXiv2023

Noise and Thermal Depinning of Wigner Crystals

We examine changes in the depinning threshold and conduction noise fluctuations for driven Wigner crystals in the presence of quenched disorder. At low temperatures there is a well defined depinning threshold and a strong peak in the noise power with $1/f$ noise characteristics. At higher temperatures, the depinning threshold shifts to lower drives and the noise, which is also reduced in power, becomes more white in character. At lower temperatures, a washboard frequency appears when the system depins elastically or forms a moving smectic state; however, this washboard signal is strongly reduced for higher temperatures and completely disappears above the melting temperature of a system without quenched disorder. Our results are in good agreement with recent transport and noise studies for systems where electron crystal depinning is believed to arise, and also show how noise can be used to distinguish between crystal, glass, and liquid phases.

cond-mat.mes-hall↗

arXiv2023

Pattern Formation and Transport for Externally Driven Active Matter on Periodic Substrates

We investigate the transport of interacting active run-and-tumble particles moving under an external drift force through a periodic array of obstacles for increasing drive amplitudes. For high activity where the system forms a motility induced phase separated state, there are several distinct dynamic phases including a low drive pinned cluster phase, an intermediate uniform fluid, and a higher drive stripe crystal state. The transitions between the phases are correlated with signatures in the transport curves, differential mobility, and power spectra of the velocity fluctuations. In contrast, in the low activity regime the transport curves and power spectra undergo little change as a function of drive. We argue that in the high activity limit, the behavior is similar to that of driven solids on periodic substrates, while in the low activity limit the system behaves like a driven fluid.

cond-mat.soft↗

arXiv2022

Melting, Reentrant Ordering and Peak Effect for Wigner Crystals with Quenched and Thermal Disorder

We consider simulations of Wigner crystals interacting with random quenched disorder in the presence of thermal fluctuations. When quenched disorder is absent, there is a well defined melting temperature determined by the proliferation of topological defects, while for zero temperature, there is a critical quenched disorder strength above which topological defects proliferate. When both thermal and quenched disorder are present, these effects compete, and the thermal fluctuations can reduce the effectiveness of the quenched disorder, leading to a reentrant ordered phase in agreement with the predictions of Nelson [Phys. Rev. B 27, 2902 (1983)]. The onset of the reentrant phase can be deduced based on changes in the transport response, where the reentrant ordering appears as an increase in the mobility or the occurrence of a depinning transition. We also find that when the system is in the ordered state and thermally melts, there is an increase in the effective damping or pinning. This produces a drop in the electron mobility that is similar to the peak effect phenomenon found in superconducting vortices, where thermal effects soften the lattice or break down its elasticity, allowing the particles to better adjust their positions to take full advantage of the quenched disorder.

cond-mat.mes-hall↗

arXiv2022

Perspective on Reversible to Irreversible Transitions in Periodic Driven Many Body Systems and Future Directions For Classical and Quantum Systems

Reversible to irreversible (R-IR) transitions arise in numerous periodically driven collectively interacting systems that, after a certain number of driving cycles, organize into a reversible state where the particle trajectories repeat, or remain irreversible with chaotic motion. R-IR transitions were first systematically studied for periodically sheared dilute colloids, and appear in a wide variety of both soft and hard matter systems, including amorphous solids, crystals, vortices in type-II superconductors, and magnetic textures. In some cases, the reversible transition is an absorbing phase transition with a critical divergence in the organization time scale. R-IR systems can store multiple memories and exhibit return point memory. We give an overview of R-IR transitions including recent advances in the field, and discuss how the general framework of R-IR transitions could be applied to a much broader class of periodically driven nonequilibrium systems, including soft and hard condensed matter systems, astrophysics, biological systems, and social systems. Some likely candidate systems are commensurate-incommensurate states, systems exhibiting hysteresis or avalanches, and nonequilibrium pattern forming states. Periodic driving could be applied to hard condensed matter systems to see if R-IR transitions occur in metal-insulator transitions, semiconductors, electron glasses, electron nematics, cold atom systems, or Bose-Einstein condensates. R-IR transitions could also be examined in dynamical systems where synchronization or phase locking occurs. We discuss the use of complex periodic driving such as changing drive directions or multiple frequencies as a method to retain complex multiple memories. Finally, we describe features of classical and quantum time crystals that could suggest the occurrence of R-IR transitions in these systems.

cond-mat.stat-mech↗

arXiv2022

Transition from Susceptible-Infected to Susceptible-Infected-Recovered Dynamics in a Susceptible-Cleric-Zombie-Recovered Active Matter Model

The Susceptible-Infected (SI) and Susceptible-Infected-Recovered (SIR) models provide two distinct representations of epidemic evolution, distinguished by the lack of spontaneous recovery in the SI model. Here we introduce a new active matter epidemic model, the ``Susceptible-Cleric-Zombie-Recovered'' (SCZR) model, in which spontaneous recovery is absent but zombies can recover with probability $γ$ via interaction with a cleric. Upon interacting with a zombie, both susceptibles and clerics can enter the zombie state with probability $β$ and $α$, respectively. By changing the intial fraction of clerics or their healing ability rate $γ$, we can tune the SCZR model between SI dynamics, in which no susceptibles or clerics remain at long times, and SIR dynamics, in which no zombies remain at long times. The model is relevant to certain real world diseases such as HIV where spontaneous recovery is impossible but where medical interventions by a limited number of caregivers can reduce or eliminate the spread of infection.

cond-mat.soft↗

arXiv2022

Bidirectional flow of two-dimensional dusty plasma under asymmetric periodic substrates driven by unbiased external excitations

Collective transport properties of a one-dimensional asymmetric periodic substrate (1DAPS) modulated two-dimensional dusty plasma (2DDP) driven by an unbiased sinusoidal excitation force are investigated using Langevin dynamical simulations. It is discovered that, by changing the amplitude and frequency of the unbiased sinusoidal external excitations, as well as the depth of 1DPAS, both the direction and speed of the persistent particle flow can be adjusted, i.e., both the flow rectification and its reversal of the ratchet effect of the steady drift motion for particles are achieved using various excitations. For the studied 2DDP under the 1DAPS, when the amplitude of the excitation increases from zero, the magnitude of the overall drift velocity increases from zero to its first maximum in the easy direction of the 1DAPS, next decreases gradually back to zero, and then increases from zero to its second maximum in the hard direction of 1DAPS before finally gradually decaying. It is found that, as the frequency of the excitation and the depth of 1DAPS change, the maximum overall drift velocity also varies, and the corresponding magnitude of the excitation varies simultaneously. The observed ratchet effect in both the easy and hard directions of 1DAPS for 2DDP is attributed to the combination of the spatial symmetry breaking of 1DAPS and the inertial effects of particles, which is further confirmed by the three different presented diagnostics.

physics.plasm-ph↗

arXiv2022

Dynamical commensuration effect in a two-dimensional Yukawa solid modulated by periodic substrates

Transverse depinning dynamics of a periodic-square-substrate modulated two-dimensional dusty plasma solid driven by a constant force in the longitudinal direction are investigated using Langevin dynamical simulations. During the increase of the commensuration ratio (the number ratio of particles to substrate potential wells), the nonmonotonic variation trend of the critical transverse depinning force is observed. It is found that the local maxima and minima of the critical transverse depinning force just correspond to the dynamical commensurate and incommensurate conditions, respectively. The dynamical commensurate effect is also clearly exhibited from the stable one-dimensional channel particle trajectories and the highly ordered structure, however, both the particle trajectories and the structure are more disordered under the incommensurate conditions. The nonmonotonic variation of the critical transverse depinning force is attributed to the stability of the lattice structure under various commensuration ratios.

physics.plasm-ph↗

arXiv2022

Magnus Induced Diode Effect for Skyrmions in Channels with Periodic Potentials

Using a particle based model, we investigate the skyrmion dynamical behavior in a channel where the upper wall contains divots of one depth and the lower wall contains divots of a different depth. Under an applied driving force, skyrmions in the channels move with a finite skyrmion Hall angle that deflects them toward the upper wall for $-x$ direction driving and the lower wall for $+x$ direction driving. When the upper divots have zero height, the skyrmions are deflected against the flat upper wall for $-x$ direction driving and the skyrmion velocity depends linearly on the drive. For $+x$ direction driving, the skyrmions are pushed against the lower divots and become trapped, giving reduced velocities and a nonlinear velocity-force response. When there are shallow divots on the upper wall and deep divots on the lower wall, skyrmions get trapped for both driving directions; however, due to the divot depth difference, skyrmions move more easily under $-x$ direction driving, and become strongly trapped for $+x$ direction driving. The preferred $-x$ direction motion produces what we call a Magnus diode effect since it vanishes in the limit of zero Magnus force, unlike the diode effects observed for asymmetric sawtooth potentials. We show that the transport curves can exhibit a series of jumps or dips, negative differential conductivity, and reentrant pinning due to collective trapping events. We also discuss how our results relate to recent continuum modeling on a similar skyrmion diode system.

cond-mat.mes-hall↗

arXiv2022

Nonlinear Dynamics, Avalanches and Noise for Driven Wigner Crystals

We consider the driven dynamics of Wigner crystals interacting with random disorder. Using numerical simulations, we find a rich variety of transport phenomena as a function of charge density, drive, and pinning strength. For weak pinning, the system forms a defect free crystal that depins elastically. When the pinning is stronger, a pinned glass phase appears that depins into a filamentary flow state, transitions at higher drives into a disordered flow phase, and finally forms a moving smectic. Within the filamentary flow phase, the conduction curves can show switching dynamics as well as negative differential conductivity in which switching events cause some flow channels to be blocked. The velocity noise in the filamentary flow regime exhibits narrow band characteristics due to the one-dimensional nature of the motion, while the moving smectic has narrow band velocity noise with a washboard frequency. In the disordered flow state, the noise power reaches a peak value and the noise has a $1/f$ character. Our transport results are consistent with recent experimental transport studies in systems where Wigner crystal states are believed to be occurring. Below the conduction threshold, we find that avalanches with a power law size distribution appear when there are sudden local rearrangements of charges from one pinned configuration to another.

cond-mat.dis-nn↗

arXiv2022

Superlubric-pinned transition of a two-dimensional solid dusty plasma under a periodic triangular substrate

The superlubric-pinned transition in the depinning dynamics of a two-dimensional (2D) solid dusty plasma modulated by 2D triangular periodic substrates is investigated using Langevin dynamical simulations. When the lattice structure of the 2D solid dusty plasma perfectly matches the triangular substrate, two distinctive pinned and moving ordered states are observed, as the external uniform driving force gradually increases from zero. When there is a mismatch between the lattice structure and the triangular substrate, however, on shallow substrates, it is discovered that all of the particles can slide freely on the substrate even when the applied driving force is tiny. This is a typical example of superlubricity, which is caused by the competition between the substrate-particle and particle-particle interactions. If the substrate depth increases further, as the driving force increases from zero, there are three dynamical states consisting of the pinned, the disordered plastic flow, and the moving ordered. In an underdense system, where there are fewer particles than potential well minima, it is found that the occurrence of the three different dynamical states is controlled by the depth of the substrate, which is quantitatively characterized using the average mobility.

physics.plasm-ph↗

arXiv2022

Pattern Formation and Flocking for Particles Near the Jamming Transition on Resource Gradient Substrates

We numerically examine a bidisperse system of active and passive particles coupled to a resource substrate. The active particles deplete the resource at a fixed rate and move toward regions with higher resources, while all of the particles interact sterically with each other. We show that at high densities, this system exhibits a rich variety of pattern forming phases along with directed motion or flocking as a function of the relative rates of resource absorption and consumption as well as the active to passive particle ratio. These include partial phase separation into rivers of active particles flowing through passive clusters, strongly phase separated states where the active particles induce crystallization of the passive particles, mixed jammed states, and fluctuating mixed fluid phases. For higher resource recovery rates, we demonstrate that the active particles can undergo motility induced phase separation, while at high densities, there can be a coherent flock containing only active particles or a solid mixture of active and passive particles. The directed flocking motion typically shows a transient in which the flow switches among different directions before settling into one direction, and there is a critical density below which flocking does not occur. We map out the different phases as function of system density, resource absorption and recovery rates,and the ratio of active to passive particles.

cond-mat.soft↗

arXiv2022

Directional Locking in a 2D Yukawa Solid Modulated by a 2D Periodic Substrate

Directional depinning dynamics of a 2D dusty plasma solid modulated by a 2D square periodic substrate are investigated using Langevin dynamical simulations. We observe prominent directional locking effects when the direction of the external driving force is varied relative to the underlying square substrate. These locking steps appear when the direction of the driving force is close to the symmetry direction of the substrate, corresponding to the different dynamical flow patterns and the structures. In the conditions between the adjacent locking steps, moving ordered states are observed. Although the discontinuous transitions often occur between the locking steps and the non-locking portion, the continuous transitions are also found around the locking step associated with the disordered plastic flow close to its termini. Our results show that directional locking also occurs for underdamped systems, which could be tested experimentally in dusty plasmas modulated by 2D substrates.

physics.plasm-ph↗

arXiv2022

Dynamic Phases and Reentrant Hall Effect for Vortices and Skyrmions on Periodic Pinning Arrays

We consider the motion of superconducting vortices and skyrmions on a square substrate near the first commensurate matching field. Slightly above commensuration, a series of dynamic phases appear including interstitial flow, and there is a transition from fluid flow to soliton flow that generates negative differential conductivity. Slightly below commensuration, vacancy depinning occurs. The dynamic phase transitions produce features in the velocity-force curves, differential mobility, and velocity fluctuations. When a Magnus force is also present, as in certain superconducting vortex or skyrmion systems, there is an expansion of the fluid state, and at lower drives there is a finite Hall angle in the fluid phase but a vanishing Hall angle in the soliton phase, giving rise to a reentrant Hall effect. We also find a regime where the Hall motion of the particles exhibits the same dynamic phases, including soliton motion at a finite angle that produces negative differential conductivity in the Hall response but not in the longitudinal response. Our results suggest that vortices driven over periodic pinning may be an ideal system for determining if a vortex Hall effect is occurring and would also be relevant for skyrmions at smaller Magnus forces.

cond-mat.supr-con↗

arXiv2022

Clogging, Diode and Collective Effects of Skyrmions in Funnel Geometries

Using a particle-based model, we examine the collective dynamics of skyrmions interacting with a funnel potential under dc driving as the skyrmion density and relative strength of the Magnus and damping terms are varied. For driving in the easy direction, we find that increasing the skyrmion density reduces the average skyrmion velocity due to jamming of skyrmions near the funnel opening, while the Magnus force causes skyrmions to accumulate on one side of the funnel array. For driving in the hard direction, there is a critical skyrmion density below which the skyrmions become trapped. Above this critical value, a clogging effect appears with multiple depinning and repinning states where the skyrmions can rearrange into different clogged configurations, while at higher drives, the velocity-force curves become continuous. When skyrmions pile up near the funnel opening, the effective size of the opening is reduced and the passage of other skyrmions is blocked by the repulsive skyrmion-skyrmion interactions. We observe a strong diode effect in which the critical depinning force is higher and the velocity response is smaller for hard direction driving. As the ratio of Magnus force to dissipative term is varied, the skyrmion velocity varies in a non-linear and non-monotonic way due to the pile up of skyrmions on one side of the funnels. At high Magnus forces, the clogging effect for hard direction driving is diminished.

cond-mat.mes-hall↗

arXiv2022

Future Directions for Active Matter on Ordered Substrates

Active matter is a term encompassing particle-based assemblies with some form of self-propulsion, including certain biological systems as well as synthetic systems such as artificial colloidal swimmers, all of which can exhibit a remarkable variety of new kinds of nonequilibrium phenomena. A wealth of non-active condensed matter systems can be described in terms of a collection of particles coupled to periodic substrates, leading to the emergence of commensurate-incommensurate effects, Mott phases, tribology effects, and pattern formation. It is natural to ask how such phases are modified when the system is active. Here we provide an overview and future directions for studying individual and collectively interacting active matter particles coupled to periodic substrates, where new types of commensuration effects, directional locking, and active phases can occur. Further directions for exploration include locking effects, the realization of active solitons or active defects in incommensurate phases, active Mott phases, active artificial spin ice, active doping transitions, active floating phases, active surface physics, active matter time crystals, and active tribology.

cond-mat.soft↗

arXiv2022

Using Active Matter to Introduce Spatial Heterogeneity to the Susceptible-Infected-Recovered Model of Epidemic Spreading

The widely used susceptible-infected-recovered (S-I-R) epidemic model assumes a uniform, well-mixed population, and incorporation of spatial heterogeneities remains a major challenge. Understanding failures of the mixing assumption is important for designing effective disease mitigation approaches. We combine a run-and-tumble self-propelled active matter system with an S-I-R model to capture the effects of spatial disorder. Working in the motility-induced phase separation regime both with and without quenched disorder, we find two epidemic regimes. For low transmissibility, quenched disorder lowers the frequency of epidemics and increases their average duration. For high transmissibility, the epidemic spreads as a front and the epidemic curves are less sensitive to quenched disorder; however, within this regime it is possible for quenched disorder to enhance the contagion by creating regions of higher particle densities. We discuss how this system could be realized using artificial swimmers with mobile optical traps operated on a feedback loop.

cond-mat.soft↗

arXiv2022

Driven Superconducting Vortex Dynamics in Systems with Two-Fold Anisotropy in the Presence of Pinning

We examine the dynamics of superconducting vortices with two-fold anisotropic interaction potentials driven over random pinning and compare the behavior under drives applied parallel and perpendicular to the anisotropy direction. The number of topological defects reaches a maximum near depinning and then drops with increasing driving force as the vortices form one-dimensional chains. This coincides with a transition from a pinned nematic to a moving smectic aligned with the soft direction of the anisotropy. The system is generally more ordered when the drive is applied along the soft direction of the anisotropy, while for driving along the hard direction, there is a critical value of the anisotropy above which the system remains aligned with the soft direction. We also observe hysteresis in the dynamics, with one-dimensional aligned chains persisting during a decreasing drive sweep to drives below the threshold for chain formation during the increasing drive sweep. More anisotropic systems have a greater amount of structural disorder in the moving state. For lower anisotropy, the system forms a moving smectic-A state, while at higher anisotropy, a moving nematic state appears instead.

cond-mat.supr-con↗

arXiv2022

Kibble-Zurek Mechanism for Nonequilibrium Phase Transitions in Driven Systems with Quenched Disorder

We numerically study the density of topological defects for a two-dimensional assembly of particles driven over quenched disorder as a function of quench rate through the nonequilibrium phase transition from a plastic disordered flowing state to a moving anisotropic crystal. A dynamical ordering transition of this type occurs for vortices in type-II superconductors, colloids, and other particle-like systems in the presence of random disorder. We find that on the ordered side of the transition, the density of topological defects $ρ_d$ scales as a power law, $ρ_d \propto 1/t_{q}^β$, where $t_{q}$ is the time duration of the quench across the transition. This type of scaling is predicted in the Kibble-Zurek mechanism for varied quench rates across a continuous phase transition. We show that scaling with the same exponent holds for varied strengths of quenched disorder. The value of the exponent can be connected to the directed percolation universality class. Our results suggest that the Kibble-Zurek mechanism can be applied to general nonequilibrium phase transitions.

cond-mat.stat-mech↗