Suppressed compressibility at large scale in jammed packings of size disperse spheres

TL;DR

This study reveals that jammed packings of size disperse spheres are hyperuniform with suppressed large-scale volume fraction fluctuations, a novel property confirmed through experiments and simulations, and applicable to various size distributions.

Contribution

The paper demonstrates that jammed packings of size disperse spheres are hyperuniform, showing suppressed large-scale fluctuations, a property not previously observed experimentally.

Findings

Packings are hyperuniform with no bulk volume fraction fluctuations.

Compressibility vanishes as wavevector approaches zero.

Derived a perturbative expression for compressibility in polydisperse systems.

Abstract

We analyze the large scale structure and fluctuations of jammed packings of size disperse spheres, produced in a granular experiment as well as numerically. While the structure factor of the packings reveals no unusual behavior for small wavevectors, the compressibility displays an anomalous linear dependence at low wavectors and vanishes when q -> 0. We show that such behavior occurs because jammed packings of size disperse spheres have no bulk fluctuations of the volume fraction and are thus hyperuniform, a property not observed experimentally before. Our results apply to arbitrary particle size distributions. For continuous distributions, we derive a perturbative expression for the compressibility that is accurate for polydispersity up to about 30%.