# Active Microrheology, Hall Effect, and Jamming in Chiral Fluids

## TL;DR

This study investigates the motion of a probe in a chiral fluid of circular swimmers, revealing nonmonotonic velocity behavior, a resonance-driven Hall angle, and jamming transitions influenced by swimmer activity and density.

## Contribution

It introduces the first analysis of Hall effect and jamming phenomena in chiral active fluids with circularly swimming particles.

## Key findings

- Probe exhibits both longitudinal and transverse motion with a Hall angle.
- Hall angle peaks at resonance between swimmer frequency and probe motion.
- Jamming occurs at high swimmer frequencies and high densities.

## Abstract

We examine the motion of a probe particle driven through a chiral fluid composed of circularly swimming disks. We find that the probe particle travels in both the longitudinal direction, parallel to the driving force, and in the transverse direction, perpendicular to the driving force, giving rise to a Hall angle. Under constant driving force, we show that the probe particle velocity in both the longitudinal and transverse directions exhibits nonmonotonic behavior as a function of the activity of the circle swimmers. The Hall angle is maximized when a resonance occurs between the frequency of the chiral disks and the motion of the probe particle. As the density of the chiral fluid increases, the Hall angle gradually decreases before reaching zero when the system enters a jammed state. We show that the onset of jamming depends on the chiral particle swimming frequency, with a fluid state appearing at low frequencies and a jammed solid occurring at high frequencies.