| We study by molecular dynamics the interplay between arrest and crystallization in hard spheres. For state points in the plane of volume fraction (0.54≤Φ≤0.63) and polydispersity (0≤s≤0.085), we delineate states that spontaneously crystallize from those that do not. No crystallization is observed for s > 0.07. For noncrystallizing (or precrystallization) samples we find isodiffusivity lines consistent with an ideal glass transition at Φg≈0.585, independent of s. Despite this, for s < 0.05, crystallization occurs at Φ>Φg. This happens on time scales for which the system is aging, and a diffusive regime in the mean square displacement is not reached; by those criteria, the system is a glass. Hence, contrary to a widespread assumption in the colloid literature, the occurrence of spontaneous crystallization within a bulk amorphous state does not prove that this state was an ergodic fluid rather than a glass. |
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