Chirality and odd mechanics in active columnar phases

TL;DR

This paper explores the unique chiral, polar, columnar phase in active materials, revealing odd elasticity, novel oscillations, and instabilities driven by activity and chirality, with implications for understanding active matter mechanics.

Contribution

It introduces a new chiral, polar, columnar phase with two-dimensional odd elasticity and derives its hydrodynamics, predicting novel oscillations and instabilities due to activity and chirality.

Findings

Identification of a chiral, polar, columnar phase with 2D odd elasticity.

Prediction of two types of non-vanishing frequency oscillations at zero wavenumber.

Discovery of buckling and helical undulation instabilities driven by activity and chirality.

Abstract

Chiral active materials display odd dynamical effects in both their elastic and viscous responses. We show that the most symmetric mesophase with two-dimensional odd elasticity in three dimensions is chiral, polar and columnar, with two-dimensional translational order in the plane perpendicular to the columns and no elastic restoring force for their relative sliding. We derive its hydrodynamic equations from those of a chiral active variant of model H. The most striking prediction of the odd dynamics is two distinct types of column oscillation whose frequencies do not vanish at zero wavenumber. In addition, activity leads to a buckling instability coming from the generic force-dipole active stress analogous to the mechanical Helfrich-Hurault instability in passive materials, while the chiral torque-dipole active stress fundamentally modifies the instability by the selection of helical column undulations.