Quasi-crystalline order in vibrated granular matter

TL;DR

This paper reports the first experimental observation of spontaneous quasi-crystal formation at the millimetric scale in vibrated granular matter, revealing new insights into non-equilibrium self-assembly processes.

Contribution

It demonstrates the first experimental realization of quasi-crystal self-assembly in a macroscopic, athermal granular system, bridging a gap between simulations and real-world observations.

Findings

Observation of 8-fold symmetric quasi-crystals in granular matter

Formation of quasi-crystals from disordered liquid-like phase

Confirmation of theoretical predictions in a non-atomic system

Abstract

Quasi-crystals are aperiodic structures that present crystallographic properties which are not compatible with that of a single unit cell. Their revolutionary discovery in a metallic alloy, less than three decades ago, has required a full reconsideration of what we defined as a crystal structure. Surprisingly, quasi-crystalline structures have been discovered also at much larger length scales in different microscopic systems for which the size of elementary building blocks ranges between the nanometric to the micrometric scale. Here, we report the first experimental observation of spontaneous quasi-crystal self-assembly at the millimetric scale. This result is obtained in a fully athermal system of macroscopic spherical grains vibrated on a substrate. Starting from a liquid-like disordered phase, the grains begin to locally arrange into three types of squared and triangular tiles that eventually align, forming 8-fold symmetric quasi-crystal that has been predicted in simulation but not yet observed experimentally in non-atomic systems. These results are not only the proof of a novel route to spontaneously assemble quasi-crystals but are of fundamental interest for the connection between equilibrium and non-equilibrium statistical physics.