Soft Sphere Packings at Finite Pressure but Unstable to Shear

TL;DR

This paper investigates the conditions under which soft sphere packings are considered jammed, revealing that common protocols often produce packings unstable to shear, and introduces a new method to generate truly jammed packings with positive shear moduli.

Contribution

The authors develop a new protocol allowing exploration of box shapes to produce genuinely jammed packings with positive shear moduli, addressing limitations of previous methods.

Findings

Common protocols produce packings unstable to shear near jamming

New protocol generates packings with strictly positive shear moduli

Shear modulus distribution exhibits novel scaling behavior

Abstract

When are athermal soft sphere packings jammed ? Any experimentally relevant definition must at the very least require a jammed packing to resist shear. We demonstrate that widely used (numerical) protocols in which particles are compressed together, can and do produce packings which are unstable to shear - and that the probability of generating such packings reaches one near jamming. We introduce a new protocol that, by allowing the system to explore different box shapes as it equilibrates, generates truly jammed packings with strictly positive shear moduli G. For these packings, the scaling of the average of G is consistent with earlier results, while the probability distribution P(G) exhibits novel and rich scaling