Density protected states in active matter under virtual confinement

TL;DR

This paper demonstrates how active nematic particles under circular illumination self-organize into boundary rings with a protected, density-independent core, revealing a robust mechanism for boundary-driven structure formation.

Contribution

It introduces a minimal model showing boundary-induced dense structures in active matter, combining simulations and hydrodynamics analysis.

Findings

Boundary rings form at the edge of circular illumination patterns.

The core density is self-selected and independent of global particle density.

The structures result from local nematic alignment and curvature-driven active currents.

Abstract

We investigate photo-responsive structure formation in a minimal model of dry active nematics. Combining microscopic simulations with the analysis of the corresponding hydrodynamic theory, we show that the system generically self-assembles into a dense, nematically ordered ring at the boundary of circular illumination patterns. Remarkably, these boundary structures give rise to a protected disordered core whose density is self-selected and independent of the global particle density. Our analysis reveals that these states emerge from a generic interplay between local nematic alignment and curvature-driven active currents. These results identify a robust route to boundary-induced structure formation in active matter and provide experimentally testable predictions.