Self-trapping of active particles with nonreciprocal interactions in disordered media

We study systems of active particles, whose perception is constrained by a vision cone, that are attracted to other particles and repelled from static obstacles. We report a novel self-trapping mechanism: active particles with nonreciprocal attraction form particle chains, which eventually become closed loops that shrink around one or many obstacles. These closed loops act as effective aggregation centers. Long-lived, self-organized closed loops require to enclose obstacles to exist. Furthermore, we find that closed loops that initially exhibit local polar order, transition to a nematic state as they absorb more particles. The unveiled mechanism corresponds to a pinning behavior that strongly hinders particle diffusion. In short, closed loops dominate the large-scale properties of active systems with nonreciprocal attraction in disordered media.