Nucleation in sheared granular matter

Author :Frank Rietz, Charles Radin, Harry L. Swinney, Matthias Schröter
Publication :Physical Review Letters
Publisher :American Physical Society
Volume :120
Number :055701
Year :2018
DOI: : 10.1103/PhysRevLett.120.055701
enclosure : 6997567 video/mp4
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.