Active surfers on a vibrating bath: self-propulsion and interactions

We present a combined experimental and theoretical investigation of a newly discovered active matter system consisting of objects floating on a vertically vibrating fluid bath. Recent experiments have demonstrated that such "surfers" oscillate vertically while self-propelling at constant horizontal velocity on the fluid interface. Multiple surfers may self-organize through the collective interfacial deformation in the form of propagating capillary waves. The experiments are complemented by a theoretical model for the surfer’s positional and orientational dynamics. The model predictions exhibit good agreement with experimentally observed interaction modes between two surfers. Generally, this work shows that self-propelling objects coupled by interfacial flows constitute a tunable platform for expanding our understanding of active systems.