Rotational transport via spontaneous symmetry breaking in vibrated disk packings

TL;DR

This study demonstrates that vibrated frictional disk packings spontaneously develop a rotational transport state through symmetry breaking, with distinct phases depending on excitation intensity, supported by experiments and simulations.

Contribution

It reveals a novel spontaneous symmetry-breaking mechanism leading to collective rotation in vibrated disk packings, supported by combined experimental and numerical evidence.

Findings

Identification of two rotational phases: LDR and MDR.

Steady rotation arises from spontaneous symmetry breaking.

Agreement between experiments and simulations confirms the phenomenon.

Abstract

It is shown that vibrated packings of frictional disks self-organize cooperatively onto a rotational-transport state where the long-time angular velocity $\bar\omega_i$ of each disk $i$ is nonzero. Steady rotation is mediated by the spontaneous breaking of local reflection symmetry, arising when the cages in which disks are constrained by their neighbors acquire quenched disorder at large packing densities. Experiments and numerical simulation of this unexpected phenomenon show excellent agreement with each other, revealing two rotational phases as a function of excitation intensity, respectively the low-drive (LDR) and the moderate-drive (MDR) regimes. In the LDR, interdisk contacts are persistent and rotation happens due to frictional sliding. In the MDR, disks bounce against each other, still forming a solid phase. In the LDR, simple energy-dissipation arguments are provided, that support the observed dependence of the typical rotational velocity on excitation strength.