Dynamics Phases, Stratification, Laning, and Pattern Formation for Driven Bidisperse Disk Systems in the Presence of Quenched Disorder

TL;DR

This study uses numerical simulations to explore the complex dynamical phases of driven bidisperse disks over quenched disorder, revealing phase separation, laning, and pattern formation influenced by driving force, packing, and size ratio.

Contribution

It uncovers how varying driving force, packing fraction, and size ratio induce diverse phases and pattern formations, including species fractionation and enhanced laning in bidisperse disk systems.

Findings

Identification of multiple dynamical phases including clogged, phase separated, and laning states.

Observation of species fractionation and pattern formation dependent on size ratio.

Enhanced laning states due to small disk clumping at specific size ratios.

Abstract

Using numerical simulations, we examine the dynamics of driven two-dimensional bidisperse disks flowing over quenched disorder. The system exhibits a series of distinct dynamical phases as a function of applied driving force and packing fraction including a phase separated state as well as a smectic state with liquid like or polycrystalline features. At low driving forces, we find a clogged phase with an isotropic density distribution, while at intermediate driving forces the disks separate into bands of high and low density with either liquid like or polycrystalline structure in the high density bands. In addition to the density phase separation, we find that in some cases there is a fractionation of the disk species, particularly when the disk size ratio is large. The species phase separated regimes form a variety of patterns such as large disks separated by chains of smaller disks. Our results show that the formation of laning states can be enhanced by tuning the ratio of disk radius of the two species, due to the clumping of small disks in the interstitial regions between the large disks.