# Nucleation in sheared granular matter

## TL;DR

This study demonstrates a first order phase transition in sheared granular spheres from disordered to ordered states, driven by homogeneous nucleation, with critical nuclei forming at a specific volume fraction.

## Contribution

It provides experimental evidence of nucleation-driven crystallization in granular matter under shear, highlighting the transition mechanism and critical nucleus size.

## Key findings

- Transition occurs at 64.5% volume fraction.
- Nucleation involves dissolution of small nuclei and growth of critical nuclei.
- Crystallites exhibit FCC and HCP symmetries.

## Abstract

We present an experiment on crystallization of packings of macroscopic granular spheres. This system is often considered to be a model for thermally driven atomic or colloidal systems. Cyclically shearing a packing of frictional spheres, we observe a first order phase transition from a disordered to an ordered state. The ordered state consists of crystallites of mixed FCC and HCP symmetry that coexist with the amorphous bulk. The transition, initiated by homogeneous nucleation, overcomes a barrier at 64.5% volume fraction. Nucleation consists predominantly of the dissolving of small nuclei and the growth of nuclei that have reached a critical size of about ten spheres.