Quasi-stable states in swarmalators: navigating the landscape of active glassy systems

In a recent work, one of us studied collective dynamics of swarmalators with delayed interactions in two dimensions. Swarmalators are particles that swarm in space, while also possessing a cyclic internal degree of freedom - oscillators that swarm. We found that adding a delay can give rise to a long breathing transient - with the radial oscillatory motion of all particles in complete synchrony, resulting in a contraction and expansion of the whole cluster. Following the transient, the system enters a quasi-stationary pseudo-crystalline state, reminding in many ways of glassy behavior. In this work, we study this state in detail. We found that during this stage, the system continues to relax via a gradual increase in global hexatic order. This increase takes place through a series of local velocity hotspots. Each hotspot alleviates local frustration, leaving behind an increased local hexatic order parameter. As the system ages, the quantity of coordination number defects in the bulk decreases, suggesting that bulk-crystallization tends to occur naturally in our 2D system. Our detailed investigation of the quasi-stable state has demonstrated an interesting mechanism of aging of an active matter system.