Abstract
Using numerical simulations, we examine the dynamics of run-and-tumble disks moving in a disordered array of fixed obstacles. As a function of increasing active disk density and activity, we find a transition from a completely clogged state to a continuous flowing phase, and in the large activity limit, we observe an intermittent state where the motion occurs in avalanches that are power law distributed in size with an exponent of . In contrast, in the thermal or low activity limit we find bursts of motion that are not broadly distributed in size. We argue that in the highly active regime, the system reaches a self-jamming state due to the activity-induced self-clustering, and that the intermittent dynamics is similar to that found in the yielding of amorphous solids. Our results show that activity is another route by which particulate systems can be tuned to a nonequilibrium critical state.
Highlights
There are numerous examples of driven collectively interacting systems that exhibit avalanches or intermittent behavior when driven over quenched disorder, including vortices in type-II superconductors [1, 2, 3], magnetic domain walls [4, 5], earthquake models [6, 7], and colloidal depinning over rough landscapes [8]
Motion often occurs in avalanches close to the depinning transition, and if depinning is associated with critical features such as diverging characteristic lengths and times, the avalanches and other fluctuating quantities will exhibit broad or power law distributions [5, 7]
Previous numerical studies [31] of active run-and-tumble disks driven though random obstacle arrays show that for fixed active disk density, the average drift mobility of the disks is a nonmonotonic function of the activity, initially increasing with increasing run length, but passing through a maximum and decreasing at large run lengths, with the onset of self-clustering or selfjamming coinciding with the mobility reduction
Summary
There are numerous examples of driven collectively interacting systems that exhibit avalanches or intermittent behavior when driven over quenched disorder, including vortices in type-II superconductors [1, 2, 3], magnetic domain walls [4, 5], earthquake models [6, 7], and colloidal depinning over rough landscapes [8]. Examples of active matter systems that have been attracting increasing attention include pedestrian flow, biological systems such as run-and-tumble bacteria, and self-propelled colloids [24, 25]. The behavior of these systems can be captured by a simple model consisting of sterically interacting hard disks with a self-mobility represented either by driven diffusion or run-and-tumble dynamics. Self-clustering occurs when multiple active disks collide and continue to swim into each other, producing an active loadbearing contact in a system containing no tensile forces, and it has been observed in experiments using self-propelled colloids [29, 30] and in simulations of disks obeying driven diffusive or run-and-tumble dynamics [28]. For a fixed run length, the mobility decreases as the active disk density increases due to crowding effects
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