Inertial Active Matter with Coulomb Friction

Area of Science:

• Physics
• Soft Matter Physics
• Granular Physics

Background:

• Friction is crucial for active matter motion, but laws differ between viscous fluids (Stokes's law) and solid contacts.
• Active particles, like bacteria or robots, often interact via solid-body friction, necessitating distinct models.

Purpose of the Study:

• To investigate the dynamics of active particles under Coulomb friction.
• To identify and characterize distinct dynamical regimes arising from the interplay of activity and friction.

Main Methods:

• Combined active granular experiments and simulations.
• Theoretical predictions to support experimental and simulation findings.

Main Results:

• Identified three distinct dynamical regimes: Brownian motion (low activity), stop-and-go (intermediate activity), and supermobile (high activity).
• Observed anomalous diffusion scaling in the supermobile regime.
• Demonstrated that these behaviors are specific to Coulomb friction and not seen with Stokesian friction.

Conclusions:

• Coulomb friction leads to rich, non-trivial dynamics in active matter systems.
• The observed regimes are characteristic of dry active objects and highlight limitations of Stokes's law for such systems.