Defect Unbinding in Active Nematics

Shankar, Suraj and Ramaswamy, Sriram and Marchetti, M Cristina and Bowick, Mark J (2018) Defect Unbinding in Active Nematics. In: PHYSICAL REVIEW LETTERS, 121 (10).

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Abstract

We formulate the statistical dynamics of topological defects in the active nematic phase, formed in two dimensions by a collection of self-driven particles on a substrate. An important consequence of the nonequilibrium drive is the spontaneous motility of strength +1/2 disclinations. Starting from the hydrodynamic equations of active nematics, we derive an interacting particle description of defects that includes active torques. We show that activity, within perturbation theory, lowers the defect-unbinding transition temperature, determining a critical line in the temperature-activity plane that separates the quasilong-range ordered (nematic) and disordered (isotropic) phases. Below a critical activity, defects remain bound as rotational noise decorrelates the directed dynamics +1/2 defects, stabilizing the quasi-long-range ordered nematic state. This activity threshold vanishes at low temperature, leading to a reentrant transition. At large enough activity, active forces always exceed thermal ones and the perturbative result fails, suggesting that in this regime activity will always disorder the system. Crucially, rotational diffusion being a two-dimensional phenomenon, defect unbinding cannot be described by a simplified one-dimensional model.

Item Type:	Journal Article
Publication:	PHYSICAL REVIEW LETTERS
Publisher:	AMER PHYSICAL SOC
Additional Information:	Copy right for this article belong to AMER PHYSICAL SOC
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	04 Oct 2018 14:46
Last Modified:	04 Oct 2018 14:46
URI:	http://eprints.iisc.ac.in/id/eprint/60808

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