Active pattern formation emergent from single-species nonreciprocity

arXiv (Cornell University)

Abstract

Nonreciprocal interactions violating Newton's third law are common in a plethora of nonequilibrium situations ranging from predator-prey systems to the swarming of birds and effective colloidal interactions under flow. While many recent studies have focused on two species with nonreciprocal coupling, less is examined for the basic single-component system breaking the actio and reactio equality of force within the same species. Here, we systematically derive a field theory for the case of single-species nonreciprocal interactions from the microscopic particle dynamics, leading to a generic continuum model termed Active Model N (N denoting nonreciprocity). We explore the rich dynamics of pattern formation in this nonreciprocal system and the emergence of self-traveling states with persistent variation and flowing of active branched patterns. One particular new characteristic pattern is an interwoven self-knitting "yarn" structure with a unique feature of simultaneous development of micro- and bulk phase separations. The growth dynamics of a "ball-of-wool" active droplet towards these self-knitted yarn or branched states exhibits a crossover between different scaling behaviors. The mechanism underlying this distinct class of active phase separation is attributed to the interplay between nonreciprocity and competition of interparticle forces. Our predictions can be applied to various biological and artificial active matter systems controlled by single-species nonreciprocity.

Authors 4

1. Zhi-Feng Huang

   Wayne State University

   Affiliation as printed

   Department of Physics and Astronomy , Wayne State University , Detroit , Michigan 48201 , USA

2. Michael te Vrugt
3. Raphael Wittkowski Aachen DWI - Leibniz Institute for Interactive Materials Department of Physics

   DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI -Leibniz Institute for Interactive Materials , 52074 Aachen , Germany

   Department of Physics , RWTH Aachen University , 52074 Aachen , Germany

4. Hartmut Löwen

   Heinrich Heine University Düsseldorf

   Affiliation as printed

   Institut für Theoretische Physik II: Weiche Materie , Heinrich-Heine-Universität Düsseldorf , 40225 Düsseldorf , Germany