Algebraic correlations and anomalous fluctuations in ordered flocks of Janus particles fueled by an AC electric field

TL;DR

This study investigates the collective behavior of Janus particles under an AC electric field, revealing long-range order, giant fluctuations, and novel statistical properties arising from polarity-velocity interactions.

Contribution

It uncovers new statistical features of ordered Janus particle flocks, including asymmetric polarity-velocity relations and algebraic polarity auto-correlation, bridging Vicsek and Active Brownian Particle physics.

Findings

Observation of true long-range order in Janus particle flocks

Detection of giant number fluctuations in the ordered state

Identification of asymmetric polarity-velocity relations and enhanced rotational diffusion

Abstract

We study the polar collective dynamics of Janus colloidal particles fueled by an AC electric field. When the density is high enough, the polar interactions between the particles induce a polar orientationally ordered state which exhibits features reminiscent of the Vicsek model such as true long-range order and giant number fluctuations. Independent measurements of the polarity and velocity at the single particle level allowed us to investigate the single particle dynamics within the ordered state. We discovered theoretically-unaddressed statistical properties of the ordered state such as the asymmetric relation of polarity and velocity, enhanced rotational diffusion stronger than in the disordered state, and an algebraic auto-correlation of the polarity. Our experimental findings, at the crossroad of the Vicsek physics and the Active Brownian Particles physics, shed light on the so-far-unexplored physics arising from the interplay between the polarity and the velocity.