This paper links the nonequilibrium glassy relaxation behavior of otherwise athermal granular materials to those of thermally activated glasses. Thus, it demonstrates a much wider universality among complex glassy materials out of equilibrium. Our three-dimensional molecular dynamics simulations, fully incorporating friction and inelastic collisions, are designed to reproduce experimental behavior of tapped granular piles. A simple theory based on a dynamics of records explains why the typical phenomenology of annealing and aging after a quench should extend to such granular matter, activated by taps, beyond the more familiar realm of polymers, colloids, and magnetic materials that all exhibit thermal fluctuations.
Paula A. Gago and Stefan Boettcher PNAS December 29, 2020 117 (52) 33072-33076; first published December 14, 2020; https://doi.org/10.1073/pnas.2012757117
[Pictured Paula A. Gago and Stefan Boettcher]. The plots show the glass transition during annealing of the granular pile at different decreases (Gamma-dot) of the tapping-strength Gamma. The snapshot shows the pile geometry at a stage during the tap, where the right side shows the grain velocities and the number of neighbors on the left (see respective color bars). [A movie of a tap is available at http://www.physics.emory.edu/faculty/boettcher/pub/tap.ogv.]
This feature is also published in Emory Report:
https://news.emory.edu/features/2021/01/esc-granular-materials/index.html