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Spatially Heterogeneous Dynamics and String-like Motion in Granular Matter and Comparison with Glass-Forming Liquids

Aaron S. Keys1, Adam R. Abate2, Sharon C. Glotzer1, and Douglas J. Durian2. (1) University of Michigan, Dept. of Chemical Engineering, 2300 Hayward Street, Ann Arbor, MI 48103-2136, (2) Dept. of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104-6396

Several attempts have been made to draw analogies between the jamming transition in granular materials and the glass transition in supercooled liquids. The two phenomena display marked similarities; both involve sudden structural arrest of the system due to its inability to sample phase space effectively. If there is indeed a link between jamming and the glass transition, then the dynamics associated with both phenomena may be related. Many of the transport properties in supercooled liquids approaching the glass transition can be rationalized in terms of spatially heterogeneous dynamics (SHD). A system is considered dynamically heterogeneous if it is possible to select a dynamically distinguishable subset of particles. The dynamics is spatially heterogeneous if that subset of particles is spatially correlated. In the present study, we present a complete characterization of SHD in an experimental system of air-driven ball bearings over a range of packing densities using several diagnostics developed for glass-forming liquids. We report striking analogies between the SHD observed in granular systems and glass-forming liquids, a result that highlights the underlying role of packing in the problem of the glass transition.