Density-mediated spin correlations drive edge-to-bulk flow transition in active chiral matter

Area of Science:

• Active matter physics
• Complex systems
• Non-equilibrium statistical mechanics

Background:

• Active chiral matter exhibits complex behaviors due to self-propulsion and chirality.
• Boundary effects significantly influence the dynamics of confined active systems.

Purpose of the Study:

• To investigate the emergence and characteristics of edge currents in active chiral matter.
• To understand how these edge currents influence bulk flow across different densities and packing fractions.

Main Methods:

• Experimental realization using spinning disk-shaped grains in a vibrating chamber.
• Systematic variation of particle density (area fraction) to observe phase transitions.
• Analysis of particle trajectories and flow fields to quantify edge currents and bulk flows.

Main Results:

• Edge currents develop due to boundary shielding across dilute (gas) to dense (crystal) regimes.
• Edge currents drive circulating bulk flows that intensify with increasing area fraction.
• A transition from boundary-localized flux to solid-body rotation occurs with increasing particle order and density.

Conclusions:

• Edge currents are a fundamental phenomenon in active chiral matter, present even in dilute systems.
• The interplay between particle interactions, density, and ordering dictates the transition from edge-dominated to bulk-dominated flow.
• A coarse-grained model successfully captures the observed flow fields, highlighting the role of collisional interlocking and emergent order.