Order-disorder transition in active nematic: A lattice model study

TL;DR

This study introduces a lattice model for active nematic systems, revealing how activity, temperature, and density influence phase transitions, including shifts in transition density and the emergence of various ordered and disordered states.

Contribution

The paper presents a novel lattice model for active nematics that captures the interplay of activity, thermal fluctuations, and density, and analyzes its phase behavior in comparison to equilibrium models.

Findings

Active nematic exhibits disordered, inhomogeneous, and bistable states.

Transition density shifts due to activity, with a jump in the order parameter.

Phase diagram constructed in the density-temperature plane.

Abstract

We introduce a lattice model for active nematic composed of self-propelled apolar particles,study its different ordering states in the density-temperature parameter space, and compare with the corresponding equilibrium model. The active particles interact with their neighbours within the framework of the Lebwohl-Lasher model, and move anisotropically along their orientation to an unoccupied nearest neighbour lattice site. An interplay of the activity, thermal fluctuations and density gives rise distinct states in the system. For a fixed temperature, the active nematic shows a disordered isotropic state, a locally ordered inhomogeneous mixed state, and bistability between the inhomogeneous mixed and a homogeneous globally ordered state in different density regime. In the low temperature regime, the isotropic to the inhomogeneous mixed state transition occurs with a jump in the order parameter at a density less than the corresponding equilibrium disorder-order transition density. Our analytical calculations justify the shift in the transition density and the jump in the order parameter. We construct the phase diagram of the active nematic in the density-temperature plane.