Granular Leidenfrost phenomenon - Density Inversion in a Granular Gas -
Abstract: In a vertically vibrated quasi-2D container filled with glass beads (d = 4.0 mm) a density inverted state is reached through a 2nd order phase transition. Above a critical shaking strength, and for a sufficient number of particles, a cluster of beads is elevated and supported by a few fast particles underneath the cluster. This cluster exhibits an almost perfect hexagonal packing, causing the density to be maximal at the floating cluster and distinctly lower above and below this cluster: a Granular Leidenfrost phenomenon. The experimental observations are confirmed by molecular dynamics simulations and a theoretical model.