Stability from activity

TL;DR

This paper demonstrates that active nematic suspensions on a substrate can maintain orientational order at high activity levels due to a new active force, challenging previous theories and revealing robust giant number fluctuations.

Contribution

It uncovers a previously unreported active force that stabilizes nematic order at high activity in suspensions on a substrate.

Findings

Active nematic suspensions can sustain order at high activity levels.

Giant number fluctuations are robust and cannot be suppressed.

Results apply broadly to biological and colloidal active matter systems.

Abstract

Suspensions of actively driven anisotropic objects exhibit distinctively nonequilibrium behaviors, and current theories predict that they are incapable of sustaining orientational order at high activity. By contrast, here we show that nematic suspensions on a substrate can display order at arbitrarily high activity due to a previously unreported, potentially stabilizing active force. The resulting nonequilibrium ordered phase displays robust giant number fluctuations that cannot be suppressed even by an incompressible solvent. Our results apply to virtually all experimental assays used to investigate the active nematic ordering of self-propelled colloids, bacterial suspensions and the cytoskeleton, and have testable implications in interpreting their nonequilibrium behaviors