Contacts Dynamics Reveals Widom Lines for Jamming

TL;DR

This study investigates the contact network dynamics near the jamming transition in granular materials, revealing Widom-like lines that connect static jamming and dynamic heterogeneities, with implications for understanding critical phenomena in granular systems.

Contribution

It experimentally demonstrates the existence of Widom lines associated with jamming, linking static and dynamic properties in granular packings under mechanical excitation.

Findings

Maximum dynamical heterogeneities occur at a packing fraction * below jamming

Two cross-overs converge at point J in the zero excitation limit

Contact network dynamics exhibit Widom-like lines near jamming

Abstract

We experimentally study the vicinity of the Jamming transition by investigating the statics and the dynamics of the contact network of an horizontally shaken bi-disperse packing of photo-elastic discs. Compressing the packing very slowly, while maintaining a mechanical excitation, yields a granular glass, namely a frozen structure of vibrating grains. In this glass phase, we observe a remarkable dynamics of the contact network, which exhibits strong dynamical heterogeneities. Such heterogeneities are maximum at a packing fraction $\phi^*$, \emph{distinct} and smaller than the jamming packing fraction $\phi_J$, which is indicated by the abrupt variation of the average number of contact per particle. We demonstrate that the two cross-overs, one for the maximum dynamical heterogeneity, and the other for static jamming, converge at point J in the zero mechanical excitation limit, a behavior reminiscent of the Widom lines in the supercritical phase of a second order critical point. Our findings are discussed in the light of recent numerical and theoretical studies of thermal soft spheres.