Enhanced orientational ordering induced by active yet isotropic bath

TL;DR

This paper reveals that active isotropic baths can enhance the orientational order of passive particles through a fluctuation-driven mechanism, challenging intuition and expanding understanding of out-of-equilibrium systems.

Contribution

It introduces a theoretical framework showing how active isotropic environments promote ordering of passive particles, supported by models and relevant for experimental testing.

Findings

Passive particles become more ordered with increased noise in active baths.

Theoretical models demonstrate fluctuation-driven ordering in active-passive systems.

Potential experimental setups to verify the predicted enhancement of order.

Abstract

Can a bath of isotropic but active particles promote ordering of anisotropic but passive particles? In this paper, we uncover a fluctuation-driven mechanism by which this is possible. Somewhat counter-intuitively, we show that the passive particles tend to be more ordered upon increasing the noise-strength of the active isotropic bath. We first demonstrate this in a general dynamical model for a non-conserved order parameter (model A) coupled to an active isotropic field and then concentrate on two examples, i. a collection of polar rods on a substrate in an active isotropic bath and ii. a passive apolar suspension in a momentum conserved, actively forced but isotropic fluid which is relevant for current research in active systems. Our theory, which is relevant for understanding ordering transitions in out-of-equilibrium systems can be tested in experiments, for instance, by introducing a low concentration of passive rod-like objects in active isotropic fluids and, since it is applicable to any non-conserved dynamical field, may have applications far beyond active matter.