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 ${\sigma }_l/{\sigma }_s=1.4$. 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, $c\lesssim 1\%$, 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.

中文翻译：

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硬盘二元混合物中六角相的消失

最近在硬盘中熔化的研究已经证实存在存在于狭窄的密度窗口中的六方晶相，该六方晶相通过一阶跃迁与各向同性液相分离，并通过连续跃迁与固相分离。但是，对于硬盘混合中的熔化情况知之甚少。在这里，我们采用量身定制的蒙特卡洛模拟方法来阐明大型（$升$）和小号（$s$）盘径比 ${\sigma }_{升}/{\sigma }_s=1.4$。我们发现，随着将小圆盘引入大圆盘系统，六方相的稳定性窗口逐渐缩小，直到连续转变线终止于终点为止，超过此终点，熔体变成一级液固转变。这种情况发生在小磁盘的浓度极低的情况下，$C\lesssim \mathrm{1个}％$，强调了六相相的易碎性。我们推测，熔化情景的变化是强烈的分馏效应的结果，我们对其性质进行了说明。