Activity-induced phase transition and coarsening dynamics in dry apolar active nematics

TL;DR

This paper explores the phase behavior and coarsening dynamics of dry apolar active nematics, revealing a first-order transition, phase coexistence, and scaling laws through simulations and theoretical analysis.

Contribution

It provides the first comprehensive phase diagram for off-lattice active nematics using Lebwohl-Lasher interactions, combining numerical, mean-field, and hydrodynamic approaches.

Findings

First-order nematic-isotropic transition with phase separation

Identification of three distinct phases based on activity and noise

Scaling exponents for nematic and density coarsening dynamics

Abstract

Using the Lebwohl-Lasher interaction for reciprocal local alignment, we present a comprehensive phase diagram for a dry, apolar, active nematic system using its stochastic \new{off-lattice} dynamics. \new{The nematic-isotropic transition in this system is first-order and occurs alongside a fluctuation-dominated phase separation.} Our phase diagram identifies three distinct regions based on activity and orientational noise relative to alignment strength: a homogeneous isotropic phase, a nematic phase with giant density fluctuations, and a coexistence region. Using mean-field analysis and hydrodynamic theory, we demonstrate that reciprocal interactions lead to a density fluctuation-induced first-order transition and derive a phase boundary consistent with numerical results. Quenching from the isotropic to nematic phase reveals coarsening dynamics where nematic ordering precedes particle clustering. Both the nematic and density fields exhibit similar scaling behaviors, exhibiting dynamic exponents $z_S \approx 2.5$ and $z_\rho \approx 2.34$, consistently falling within the range of 2 and 3.