The pseudo-two-dimensional dynamics in a system of macroscopic rolling spheres

TL;DR

This paper investigates the complex quasi-two-dimensional dynamics of fluidized macroscopic spheres, revealing rich phases including coexistence of melting hexagonal crystals with liquids, differing from purely 2D systems.

Contribution

It demonstrates the emergence of multiple phases and phase coexistence in a quasi-2D system of fluidized spheres, highlighting novel dynamical behaviors not seen in purely 2D setups.

Findings

Observation of gas, liquid, glass, and hexagonal crystal phases.

Melting of hexagonal crystals occurs with liquid coexistence.

Distinct phase behavior compared to purely 2D systems.

Abstract

We study in this work the dynamics of a collection of identical hollow spheres (ping-pong balls) that rest on a horizontal metallic grid. Fluidization is achieved by means of a turbulent air current coming from below. The upflow is adjusted so that the particles do not levitate over the grid, resulting in quasi-two-dimensional dynamics. We show that the behavior of diffusion and correlations in this system is particularly rich. Noticeably as well (and related to the complex dynamical behavior), a variety of phases appear, with important peculiarities with respect to analogous setups. We observe gas, liquid, glass, and hexagonal crystal phases. Most notably, we show that the melting of the hexagonal crystal occurs in coexistence with a liquid phase. This strikingly differs from the corresponding transition in a purely two-dimensional systems of air-fluidized disks, for which no phase coexistence has been reported in the literature.