Crystallization of confined non-Brownian spheres by vibrational annealing.

We introduce an experimental method to crystallize ensembles of non-Brownian spheres confined in narrow containers. The method is based on programmed vibrations and a cooling procedure (annealing). Starting with a granular gas, the system slowly relaxes into a solid ordered structure: Body-centered-tetragonal and face-centered-cubic single crystals are obtained depending on the dimensions of the capillaries. Dry and lubricated beads behave differently, indicating that a sticking coefficient between the particles is important in the dynamics of the crystallization.