Frank Rietz, Charles Radin, Harry L. Swinney, and Matthias Schroeter
Nucleation in Sheared Granular Matter
(961K, pdf)

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.