Spontaneous spirals in vibrated granular chains

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We present experimental measurements on the spontaneous formation of compact spiral structures in vertically-vibrated granular chains. Under weak vibration, when the chain is quasi two-dimensional and self-avoiding, spiral structures emerge from generic initial configurations. We compare geometrical characteristics of the spiral with that of an ideal tight spiral. Globally, the spiral undergoes a slow rotation such that to keep itself wound, while internally, fast vibrational modes are excited along the backbone with transverse oscillations dominating over longitudinal ones. Spirals have an extremely small volume in phase space, and hence, their formation demonstrates how nonequilibrium dynamics can result in a nonuniform sampling of phase space.