Xiaqing Shi
University of Suzhou, China
Fragility, condensation and synchronization in aligning chiral active matter
I will present in this talk the susceptibility of long-range ordered phases of two-dimensional dry aligning active matter to population disorder, taken in the form of a distribution of intrinsic individual chiralities. Using a combination of particle-level models and hydrodynamic theories derived from them, we show that while in finite systems all ordered phases resist a finite amount of such chirality disorder, the homogeneous ones (polar flocks and active nematics) are unstable to any amount of disorder in the infinite-size limit.[1] I will further 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.[2] 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.
References:
[1] Ventejou, B., Chaté, H., Montagne, R. & Shi, X. Susceptibility of Orientationally Ordered Active Matter to Chirality Disorder. Phys. Rev. Lett. 127, 238001 (2021).
[2] Wang, Y., Ventejou, B., Chate, H. & Shi, X. Condensation and Synchronization in Aligning Chiral Active Matter. Phys. Rev. Lett. 133, 258302 (2024)
