Oscillations of a hydrodynamic crystal lattice

When brought into close proximity, two or more droplets bouncing on a vertically vibrating fluid bath exhibit a rich spectrum of dynamical behaviour. In particular, pairs of such droplets have been shown to destabilize into oscillatory, orbiting, and promenading modes, while a collection of multiple droplets can form crystal-like lattices with highly regular structure. In this talk, we present the results of a combined experimental and theoretical study in we characterize and rationalize the behaviour of a circular chain of bouncing drops, reminiscent of a one-dimensional crystal lattice. As the vibrational forcing is increased, the stationary chain first destabilizes into an oscillatory mode and then into a striking soliton-like disturbance, before ``melting'' at sufficiently high acceleration of the bath. Similarities with models such as the Toda lattice, used to model crystal vibrations in solid-state physics, are discussed.