Disappearance of the Hexatic Phase in a Binary Mixture of Hard Disks

John Russo, Nigel Wilding

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Recent studies of melting in hard disks have confirmed the existence of a hexatic phase occurring in a narrow window of density which is separated from the isotropic liquid phase by a first-order transition, and from the solid phase by a continuous transition. However, little is known concerning the melting scenario in mixtures of hard disks. Here we employ tailored Monte Carlo simulations to elucidate the phase behavior of a system of large (l) and small (s) disks with diameter ratio σl/σs=1.4. We find that as small disks are introduced to a system of large ones, the stability window of the hexatic phase shrinks progressively until the line of continuous transitions terminates at an end point beyond which melting becomes a first-order liquid-solid transition. This occurs at surprisingly low concentrations of the small disks, c≲1%, emphasizing the fragility of the hexatic phase. We speculate that the change to the melting scenario is a consequence of strong fractionation effects, the nature of which we elucidate.
Original languageEnglish
Article number115702
Pages (from-to)1-5
Number of pages5
JournalPhysical Review Letters
Issue number11
Early online date14 Sept 2017
Publication statusPublished - 15 Sept 2017


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