Extreme active matter at high densities.

Area of Science:

• Physics of complex systems
• Soft matter physics
• Statistical mechanics

Background:

• Dense active matter, composed of self-propelled particles, displays unique collective behaviors.
• Understanding phase transitions and emergent phenomena in these systems is crucial.
• Previous studies explored aspects of active matter, but a unified view of its diverse behaviors is lacking.

Purpose of the Study:

• To investigate the behavior of dense active matter across a range of particle persistence times and propulsion forces.
• To characterize the transitions between different dynamical states, including glass, jamming, and turbulence.
• To elucidate the underlying mechanisms of intermittency and plastic deformation in active matter.

Main Methods:

• Simulations of dense active matter at large Péclet numbers.
• Systematic variation of particle persistence time (τp) and propulsion force (f).
• Analysis of density relaxations, stress distributions, and particle dynamics.

Main Results:

• At low persistence times (τp → 0), decreasing force (f) leads to a glass transition.
• At high persistence times (τp → ∞), decreasing force (f) results in jamming with stress along force-chains.
• Intermediate persistence times exhibit intermittency with jamming-yielding bursts and Eshelby deformations.
• Increasing force (f) enhances burst frequency, leading to vorticity and turbulence.

Conclusions:

• Dense active matter unifies physics of glass, jamming, plasticity, and turbulence.
• A new state of driven classical matter emerges with rich dynamical behaviors.
• The study provides a comprehensive framework for understanding active matter under varying conditions.