Density Induced Phases in Active Nematic

TL;DR

This paper models active nematic particles on a 2D substrate, revealing how density influences phase transitions, including first order and bistable states, providing insights into complex biological systems.

Contribution

It introduces a minimal lattice model for active nematics and explores their phase behavior across different densities, highlighting novel transition phenomena.

Findings

First order transition from isotropic to banded state at low density

Plateau in scalar order parameter over a density range

Bistability between homogeneous and inhomogeneous states at high density

Abstract

We introduce a minimal model for a collection of self-propelled apolar active particles, also called as `active nematic', on a two-dimensional substrate and study the order-disorder transition with the variation of density. The particles interact with their neighbours within the framework of the Lebwohl-Lasher model and move asymmetrically, along their orientation, to unoccupied nearest neighbour lattice sites. At a density lower than the equilibrium isotropic-nematic transition density, the active nematic shows a first order transition from the isotropic state to a banded state. The banded state extends over a range of density, and the scalar order parameter of the system shows a plateau like behaviour, similar to that of the magnetic systems. In the large density limit the active nematic shows a bistable behaviour between a homogeneous ordered state with global ordering and an inhomogeneous mixed state with local ordering. The study of the above phases with density variation is scant and gives significant insight of complex behaviours of many biological systems.