Odd mobility of a passive tracer in a chiral active fluid

TL;DR

This paper introduces a generalized Green-Kubo relation for the odd mobility of a passive tracer in a chiral active fluid, revealing size-dependent transport properties and potential for particle separation.

Contribution

It develops a novel response theory for anomalous lift in chiral active fluids and validates it through molecular dynamics simulations.

Findings

Asymmetric tracer mobility can be mechanically understood.

Odd and even mobility components decay differently with size.

Size-based particle separation is feasible using chiral active fluids.

Abstract

Chiral active fluids break both time-reversal and parity symmetry, leading to exotic transport phenomena unobservable in ordinary passive fluids. We develop a generalized Green-Kubo relation for the anomalous lift experienced by a passive tracer suspended in a two-dimensional chiral active fluid subjected to an applied force. This anomalous lift is characterized by a transport coefficient termed the odd mobility. We validate our generalized response theory using molecular dynamics simulations, and we show that the asymmetric tracer mobility may be understood mechanically in terms of asymmetric deformations of the tracer-fluid density distribution function. We show that the even and odd components of the mobility decay at different rates with tracer size, suggesting the possibility of size-based particle separation using a chiral active working fluid.