Live Soap: Order, Fluctuations and Instabilities in Active Smectics

TL;DR

This paper develops a hydrodynamic theory for active smectics, predicting order, instabilities, and phase transitions in different dimensions, extending previous results to all dynamical regimes.

Contribution

It provides a comprehensive hydrodynamic framework for active smectics, including new predictions on order, instabilities, and phase behavior across dimensions.

Findings

Quasi-long-ranged order in 2D, long-range in 3D

Kosterlitz-Thouless transition to active nematics

Suppression of giant number fluctuations by smectic elasticity

Abstract

We construct a hydrodynamic theory of noisy, apolar active smectics, in bulk suspension or on a substrate. Our predictions include: quasi-long-ranged smectic order in dimension d = 2, and long- ranged in d = 3, extending previously published results to all dynamical regimes; Kosterlitz-Thouless melting to an active nematic at high and low concentrations in d = 2; nonzero second-sound speed parallel to the layers; the suppression of giant number fluctuations by smectic elasticity; instability to spontaneous undulation and flow in bulk contractile smectics; a layer spacing instability, possibly oscillatory, for large enough extensile active stresses.