Dynamic Phases and Combing Effects for Elongated Particles Moving Over Quenched Disorder

TL;DR

This study explores how elongated particles driven over disordered landscapes exhibit diverse dynamic phases, with pinning enhancing alignment and leading to complex states like clustering and clogging, depending on system parameters.

Contribution

It introduces a detailed analysis of dynamic phases of elongated particles over quenched disorder, highlighting the combing effect and nonmonotonic nematic ordering.

Findings

Pinning can enhance particle alignment, creating a maximum in nematic order.

Different dynamic regimes include stripe, combed, and clogged states.

High pinning leads to heterogeneous clustering and high diffusion states.

Abstract

We consider a two-dimensional system of elongated particles driven over a random quenched disorder landscape. For varied pinning site density, external drive magnitude, and particle elongation, we find a wide variety of dynamic phases, including random structures, stripe or combed phases with nematic order, and clogged states. The different regimes can be identified by examining nematic ordering, cluster size, number of pinned particles, and transverse diffusion. In some regimes we find that the pinning can enhance the particle alignment, producing a nonmonotonic signature in the nematic ordering with a maximum at a particular combination of pinning density and drive. The optimal nematic occurs when a sufficient number of particles can be pinned, generating a local shear and leading to what we call a combing effect. At high drives, the combing effect is reduced when the number of pinned particles decreases. For stronger pinning, the particles form a heterogeneous clustered or clogged state that depins into a fluctuating state with high diffusion.