Spontaneous Velocity Alignment in Motility-Induced Phase Separation.

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Self-propelled particles exhibit complex behaviors like motility-induced phase separation (MIPS).
• Understanding emergent order in systems lacking explicit alignment is crucial.

Purpose of the Study:

• To investigate the emergence of velocity order during MIPS in purely repulsive self-propelled particles.
• To identify the underlying mechanism responsible for velocity alignment in the absence of explicit interactions.

Main Methods:

• Simulations of purely repulsive spherical self-propelled particles.
• Analysis of particle clustering and velocity correlations.
• Quantification using spatial correlation functions.

Main Results:

• MIPS is accompanied by growing order in particle velocities.
• Particles form aligned or vortex-like domains.
• Domain size increases with self-propulsion persistence.

Conclusions:

• A hidden Vicsek-like alignment interaction emerges from steric interactions and self-propulsion.
• This emergent interaction drives the observed velocity alignment and domain formation during MIPS.