Condensation and Synchronization in Aligning Chiral Active Matter

TL;DR

This paper demonstrates that dense chiral active matter systems can spontaneously form condensates like vortices, leading to synchronization, which contrasts with typical phase separation in 2D active matter.

Contribution

It reveals a novel condensation phenomenon in aligning chiral active matter, showing how vortices and polar packets form and absorb particles, with a new phenomenological theory explaining these results.

Findings

Condensates can absorb a finite fraction of particles.

Condensates maintain finite or slowly growing size.

Synchronization occurs despite local interactions in 2D.

Abstract

We show that spontaneous density segregation in dense systems of aligning circle swimmers is a condensation phenomenon at odds with the phase separation scenarios usually observed in two-dimensional active matter. The condensates, which take the form of vortices or rotating polar packets, can absorb a finite fraction of the particles in the system, and keep a finite or slowly growing size as their mass increases. Our results are obtained both at particle and continuous levels. We consider both ferromagnetic and nematic alignment, and both identical and disordered chiralities. Condensation implies synchronization, even though our systems are in 2D and bear strictly local interactions. We propose a phenomenological theory based on observed mechanisms that accounts qualitatively for our results.