Solid particles walking on a vibrating interface: Towards wave-mediated granular matter (2024)
Undergraduate: Haoyu Ma
Faculty Advisor: Pedro Saenz
Department: Applied Math
The timeless pastime of stone-skipping encapsulates the difficulty in keeping a solid object bouncing across a liquid surface as energy is dissipated with each impact. Of the methods devised for the sustained bouncing of particles, vertical excitation of the liquid bath has proved notably effective. One remarkable example is walking droplets, wherein millimetric droplets "walk" on a vibrating liquid bath through a resonant interaction with their own wave field, and whose unique wave-particle duality catalyzed the emergence of the nascent field of pilot-wave hydrodynamics. Yet, despite significant efforts, walkers have remained thus far exclusively comprised of liquid droplets, inhibiting study of emergent collective dynamics as head-on collisions are not permitted due to coalescence. Here, we present a new pilot-wave system, in which a solid walker replaces its liquid predecessor and self-propels on a liquid-liquid interface. This new system enables the heretofore prohibited direct collisions between particles, thus pushing the relevance of pilot-wave hydrodynamics beyond single-particle systems. Notably, solid walkers also represent the potential of creating a new class of granular material, in which interactions between particles are mediated by their "pilot" wave fields.