# Reversibility, Pattern Formation and Edge Transport in Active Chiral and Passive Disk Mixtures

## TL;DR

This study explores how mixtures of active and passive disks organize and transport under various conditions, revealing reversible states, phase separation, and edge transport phenomena influenced by chirality and drive parameters.

## Contribution

It introduces a detailed numerical analysis of active-passive disk mixtures, uncovering phase behaviors, reversibility transitions, and edge transport mechanisms not previously characterized.

## Key findings

- Reversible labyrinth states at low densities and small orbit radii.
- Divergence in cycles to reach steady state at a critical orbit radius.
- Edge transport along phase boundaries influenced by chirality.

## Abstract

We numerically examine mixtures of circularly moving and passive disks as a function of density and active orbit radius. For low or intermediate densities and/or small orbit radii, the system can organize into a reversible partially phase separated labyrinth state in which there are no collisions between disks, with the degree of phase separation increasing as the orbit radius increases. As a function of orbit radius, we find a divergence in the number of cycles required to reach a collision-free steady state at a critical radius, while above this radius the system remains in a fluctuating liquid state. For high densities, the system can organize into a fully phase separated state that is mostly reversible, but collisions at the boundaries between the phases lead to a net transport of disks along the boundary edges in a direction determined by the chirality of the active disk orbits. We map the dynamic phases as a function of density and orbit radii, and discuss the results in terms of the reversible-irreversible transition found in other periodically driven non-thermal systems. We also consider mixtures of circularly driven disks and ac driven disks where the ac drive is either in or out of phase with the circular motion, and find a rich variety of pattern forming and reentrant disordered phases.