Non-equilibrium two-phase coexistence in a confined granular layer

TL;DR

This study observes non-equilibrium two-phase coexistence in a vibrated granular layer, revealing steady-state crystal-liquid coexistence with notable temperature differences, driven by entropy considerations despite non-equilibrium effects.

Contribution

It demonstrates the formation of stable two-layer crystal and liquid phases in a vibrated granular system, highlighting non-equilibrium phenomena analogous to equilibrium phase behavior.

Findings

Two-layer crystals with square symmetry coexist with granular liquid.

A critical vibration amplitude triggers phase coexistence.

Significant temperature differences exist between phases.

Abstract

We report the observation of the homogenous nucleation of crystals in a dense layer of steel spheres confined between two horizontal plates vibrated vertically. Above a critical vibration amplitude, two-layer crystals with square symmetry were found to coexist in steady state with a surrounding granular liquid. By analogy to equilibrium hard sphere systems, the phase behavior can be explained through entropy maximization. However, dramatic non-equilibrium effects are present, including a significant difference in the granular temperatures of the two phases.