# Glassy swirls of active dumbbells

## TL;DR

This study investigates how active propulsion influences glass formation in dense dumbbell mixtures, revealing distinct dynamical behaviors and heterogeneities compared to temperature-induced glasses, with implications for biological systems.

## Contribution

It demonstrates that activity induces a unique glass transition characterized by large swirling vortices, differing fundamentally from thermal glasses.

## Key findings

- Activity-induced glass shows large vortices.
- Dynamical heterogeneity differs between thermal and active glasses.
- Swirling vortex scale diverges near the glass transition.

## Abstract

The dynamics of a dense binary mixture of soft dumbbells, each subject to an active propulsion force and thermal fluctuations, shows a sudden arrest, first to a translational then to a rotational glass, as one reduces temperature $T$ or the self-propulsion force $f$. Is the temperature-induced glass different from the activity-induced glass? To address this question, we monitor the dynamics along an iso-relaxation-time contour in the $(T-f)$ plane. We find dramatic differences both in the fragility and in the nature of dynamical heterogeneity which characterise the onset of glass formation - the activity-induced glass exhibits large swirls or vortices, whose scale is set by activity, and appears to diverge as one approaches the glass transition. This large collective swirling movement should have implications for collective cell migration in epithelial layers.