Vibrated polar disks: spontaneous motion, binary collisions, and collective dynamics

TL;DR

This study investigates the behavior of vibrated polar disks, revealing their spontaneous motion, collision dynamics, and collective behavior, demonstrating ordered phases and density effects in a controlled dry active matter system.

Contribution

We introduce a system of vibrated polar disks that exhibit collective motion and analyze their collision and alignment behaviors, advancing understanding of dry active matter dynamics.

Findings

Disks move coherently along their polarity direction.

Binary collisions lead to weak effective alignment.

Ordered collective motion with large orientational domains.

Abstract

We study the spontaneous motion, binary collisions, and collective dynamics of "polar disks", i.e. purpose-built particles which, when vibrated between two horizontal plates, move coherently along a direction strongly correlated to their intrinsic polarity. The motion of our particles, although nominally three-dimensional and complicated, is well accounted for by a two-dimensional persistent random walk. Their binary collisions are spatiotemporally extended events during which multiple actual collisions happen, yielding a weak average effective alignment. We show that this well-controlled, "dry active matter" system can display collective motion with orientationally-ordered regions of the order of the system size. We provide evidence of strong number density in the most ordered regimes observed. These results are discussed in the light of the limitations of our system, notably those due to the inevitable presence of walls.