Spontaneous velocity alignment in Motility-induced Phase Separation

Abstract

We study a system of purely repulsive spherical self-propelled particles in the minimal set-up inducing Motility-Induced Phase Separation (MIPS). We show that, even if explicit alignment interactions are absent, a growing order in the velocities of the clustered particles accompanies MIPS. Particles arrange into aligned or vortex-like domains. Their sizes increase as the persistence of the self-propulsion grows, an effect that is quantified studying the spatial correlation function of the velocities. We explain the velocity-alignment by unveiling a hidden alignment interaction of the Vicsek-like form, induced by the interplay between steric interactions and self-propulsion. As a consequence, we argue that the MIPS transition cannot be fully understood in terms of a scalar field, the density, since the collective orientation of the velocities should be included in effective coarse-grained descriptions.

First submission to the journal: 1 October, 2019

References in corpus (18)

• Novel type of phase transition in a system of self-driven particles
• Self-motile colloidal particles: from directed propulsion to random walk
• Interaction Ruling Animal Collective Behaviour Depends on Topological rather than Metric Distance: Evidence from a Field Study
• Motility-Induced Phase Separation
• Statistical Mechanics of Interacting Run-and-Tumble Bacteria
• When are active Brownian particles and run-and-tumble particles equivalent? Consequences for motility-induced phase separation
• Non-equilibrium clustering of self-propelled rods
• Pressure and Phase Equilibria in Interacting Active Brownian Spheres
• Collective motion and nonequilibrium cluster formation in colonies of gliding bacteria
• Emergent vortices in populations of colloidal rollers
• Effective Interactions in Active Brownian Suspensions
• From Phase to Micro-Phase Separation in Flocking Models: The Essential Role of Non-Equilibrium Fluctuations
• Finite-size scaling as a way to probe near-criticality in natural swarms
• Swarm behavior of self-propelled rods and swimming flagella
• Active colloidal suspensions: Clustering and phase behavior
• Motility-induced phase separation and coarsening in active matter
• Active escape dynamics: the effect of persistence on barrier crossing
• Applicability of Effective Pair Potentials for Active Brownian Particles

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• Mean area of the convex hull of a run and tumble particle in two dimensions
• Run-and-Tumble particle in inhomogeneous media in one dimension
• Active matter in infinite dimensions: Fokker-Planck equation and dynamical mean-field theory at low density