Collective behavior of active molecules: Dynamic clusters, holes, and active fractalytes

Abstract

Recent experiments have led to active colloidal molecules, which aggregate from nonmotile building blocks and acquire self-propulsion through their nonreciprocal interactions. Here, we model the collective behavior of such active molecules and predict, besides dynamic clusters, the existence of a so-far unknown state of active matter made of "active fractalytes", which are motile crystallites featuring internal holes, gaps, and a fractal dimension. These structures could serve as a starting point for the creation of active materials with a low density and mechanical properties that can be designed through their fractal internal structure.