# Dynamical self-assembly of dipolar active Brownian particles in two dimensions

## TL;DR

This study uses Brownian Dynamics simulations to investigate how active dipolar particles self-assemble in two dimensions, revealing phenomena like chain formation, phase separation suppression, and flocking behavior depending on motility and interaction strength.

## Contribution

It introduces a comprehensive analysis of active dipolar particles, highlighting the emergence of flocking and the suppression of phase separation due to dipolar interactions.

## Key findings

- Dipolar particles form chains at low motility and density.
- High motility breaks chains, leading to isotropic fluids.
- Strong dipolar coupling suppresses phase separation and induces flocking.

## Abstract

Based on Brownian Dynamics (BD) simulations, we study the dynamical self-assembly of active Brownian particles with dipole-dipole interactions, stemming from a permanent point dipole at the particle center. The propulsion direction of each particle is chosen to be parallel to its dipole moment. We explore a wide range of motilities and dipolar coupling strengths and characterize the corresponding behavior based on several order parameters. At low densities and low motilities, the most important structural phenomenon is the aggregation of the dipolar particles into chains. Upon increasing the particle motility, these chain-like structures break, and the system transforms into a weakly correlated isotropic fluid. At high densities, we observe that the motility-induced phase separation is strongly suppressed by the dipolar coupling. Once the dipolar coupling dominates the thermal energy, the phase separation disappears, and the system rather displays a flocking state, where particles form giant clusters and move collective along one direction. We provide arguments for the emergence of the flocking behavior, which is absent in the passive dipolar system.