Capillary surfers: Wave-driven particles at a vibrating fluid interface

A small solid particle resting atop a vibrating fluid interface generates a field of outwardly propagating capillary waves due to its relative vertical motion. In this paper, we show that if the particle's symmetry is broken, the resultant unbalanced wave stresses enable steady self-propulsion along the interface. Such ``capillary surfers'' interact with each other hydrodynamically at long range via their mutual wavefield and form a number of dynamic bound states. This new active system bridges the gap between dissipation- and inertia-dominated regimes and promises a number of novel collective behaviors.