Metastability of Discrete-Symmetry Flocks

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Metastability of Discrete-Symmetry Flocks

Brieuc Benvegnen, Omer Granek, Sunghan Ro, Ran Yaacoby, Hugues Chaté, Yariv Kafri, David Mukamel, Alexandre Solon, and Julien Tailleur

Phys. Rev. Lett. 131, 218301 – Published 22 November 2023

Abstract

We study the stability of the ordered phase of flocking models with a scalar order parameter. Using both the active Ising model and a hydrodynamic description, we show that droplets of particles moving in the direction opposite to that of the ordered phase nucleate and grow. We characterize analytically this self-similar growth and demonstrate that droplets spread ballistically in all directions. Our results imply that, in the thermodynamic limit, discrete-symmetry flocks—and, by extension, continuous-symmetry flocks with rotational anisotropy—are metastable in all dimensions.

Received 1 June 2023
Accepted 23 October 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.218301

Physics Subject Headings (PhySH)

Flocking

Collective dynamics Living matter & active matter

Theories of collective dynamics & active matter

Polymers & Soft MatterStatistical Physics & Thermodynamics

Authors & Affiliations

Brieuc Benvegnen¹, Omer Granek ², Sunghan Ro ³, Ran Yaacoby ², Hugues Chaté ^4,5,1, Yariv Kafri ², David Mukamel ⁶, Alexandre Solon ¹, and Julien Tailleur ³

¹Sorbonne Université, CNRS, Laboratoire de Physique Théorique de la Matière Condensée, 75005 Paris, France
²Department of Physics, Technion–Israel Institute of Technology, Haifa 32000, Israel
³Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
⁴Service de Physique de l’Etat Condensé, CEA, CNRS, Université Paris-Saclay, CEA-Saclay, 91191 Gif-sur-Yvette, France
⁵Computational Science Research Center, Beijing 100094, China
⁶Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel