Crystallization of Self-Propelled Hard Discs

We experimentally study the crystallization of a monolayer of vibrated discs with a built-in polar asymmetry, a model system of active liquids, and contrast it with that of vibrated isotropic discs. Increasing the packing fraction ϕ, the quasicontinuous crystallization reported for isotropic discs i...

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Bibliographic Details
Published in:Physical review letters 2016-08, Vol.117 (9), p.098004-098004, Article 098004
Main Authors: Briand, G, Dauchot, O
Format: Article
Language:English
Subjects:
Binding energy (nuclear)
Clusters
Condensed Matter
Crystallization
Disks
Droplets
Dynamical systems
Liquids
Melts
Physics
Soft Condensed Matter
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Summary:We experimentally study the crystallization of a monolayer of vibrated discs with a built-in polar asymmetry, a model system of active liquids, and contrast it with that of vibrated isotropic discs. Increasing the packing fraction ϕ, the quasicontinuous crystallization reported for isotropic discs is replaced by a transition, or a crossover, towards a "self-melting" crystal. Starting from the liquid phase and increasing the packing fraction, clusters of dense hexagonal-ordered packed discs spontaneously form, melt, split, and merge, leading to a highly intermittent and heterogeneous dynamics. For a packing fraction larger than ϕ^{*}, a few large clusters span the system size. The cluster size distribution is monotonically decreasing for ϕϕ^{*}, and is a power law at the transition. The system is, however, never dynamically arrested. The clusters permanently melt from place to place, forming droplets of an active liquid which rapidly propagate across the system. This self-melting crystalline state subsists up to the highest possible packing fraction, questioning the stability of the crystal for active discs unless it is at ordered close packing.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.117.098004