The first jamming crossover: geometric and mechanical features

TL;DR

This paper investigates the structural and mechanical changes in particle systems during the first jamming crossover, revealing how these transitions influence force networks, vibrational modes, and system softening.

Contribution

It provides a detailed analysis of the structural and mechanical evolution at the first jamming crossover, linking it to density anomalies and force network rearrangements.

Findings

First jamming crossover occurs at a specific volume fraction.

Rearrangement of force networks causes system softening.

Normal mode density of states and spatial properties change qualitatively.

Abstract

The jamming transition characterizes athermal systems of particles interacting via finite range repulsive potentials, and occurs on increasing the density when particles cannot avoid making contacts with those of their first coordination shell. We have recently shown [M. Pica Ciamarra and P. Sollich, arXiv:1209.3334] that the same systems are also characterized by a series of jamming crossovers. These occur at higher volume fractions as particles are forced to make contact with those of subsequent coordination shells. At finite temperature, the crossovers give rise to dynamic and thermodynamic density anomalies, including a diffusivity anomaly and a negative thermal expansion coefficient. Density anomalies may therefore be related to structural changes occurring at the jamming crossovers. Here we elucidate these structural changes, investigating the evolution of the structure and of the mechanical properties of a jammed system as its volume fraction varies from the jamming transition to and beyond the first jamming crossover. We show that the first jamming crossover occurs at a well defined volume fraction, and that it induces a rearrangement of the force network causing a softening of the system. It also causes qualitative changes in the normal mode density of states and the spatial properties of the normal mode vectors.