Glass Transition in Supercooled Liquids with Medium-Range Crystalline Order (original) (raw)

2018, Physical Review Letters

The origins of rapid dynamical slow down in glass forming liquids in the growth of static length scales, possibly associated with identifiable structural ordering, is a much debated issue. Growth of medium range crystalline order (MRCO) has been observed in various model systems to be associated with glassy behaviour. Such observations raise the question about the eventual state reached by a glass former, if allowed to relax for sufficiently long times. Is a slowly growing crystalline order responsible for slow dynamics? Are the molecular mechanisms for glass transition in liquids with and without MRCO the same? If yes, glass formers with MRCO provide a paradigm for understanding glassy behaviour generically. If not, systems with MRCO form a new class of glass forming materials whose molecular mechanism for slow dynamics may be easier to understand in terms of growing crystalline order, and should be approached in that manner, even while they will not provide generic insights. In this study we perform extensive molecular dynamics simulations of a number of glass forming liquids in two dimensions and show that the static and dynamic properties of glasses with MRCO are different from other glass forming liquids with no predominant local order. We also resolve an important issue regarding the so-called Point-to-set method for determining static length scales, and demonstrate it to be a robust, order agnostic, method for determining static correlation lengths in glass formers. Recently, in a series of papers Tanaka et. al. [9-11] showed that the glass transition in systems with MRCO is determined by the length scale associated with that of locally preferred structures. For example, for two dimensional systems, the correlation length associated with hexatic order is the important length scale and the glass transition in these systems are completely controlled by the hexatic correlation length. In [12], a polydisperse two dimensional glass forming liquid was studied in which the hexatic correlation grows rapidly with increasing packing fraction. The dynamic heterogeneity [13-15] length scale obtained from the scaling analysis of the wave-vector (q) dependence of the four-point structure factor, S 4 (q, t)