Mixing effects in the crystallization of supercooled quantum binary liquid mixtures

The study of crystallization in supercooled liquids is important not only for understanding the fundamental mechanisms of crystal growth, but also to investigate the nature of the glass transition. The simplest systems that can be used as test beds for our current microscopic understanding of the behavior of supercooled liquids are binary mixtures. Liquid binary mixtures are generally harder to crystallize compared to pure fluids, showing a very rich, yet not fully understood behavior in dependence of particle size ratio and composition. For example, understanding why for some compositions certain binary metallic mixtures invariably form crystal phases that compete with glass formation in terms of stability is an open and fundamental question for understanding both crystallization and its interplay with glass-forming ability. While the effects of mixing have been widely investigated by classical molecular dynamics simulations of particles interacting through a simple Lennard-Jones (LJ) potential, comparable experimental studies have so far remained out of reach. Here I will present experimental data on the crystallization kinetics of supercooled binary mixtures of parahydrogen, orthodeuterium, and neon obtained by employing the liquid microjet technique originally developed for the production of high-density internal targets at storage rings. By starting with a pure substance the crystallization slows down considerably by increasing the amount of the impurity species. I will show that a possible explanation of this surprising behavior has its origin in quantum effects that play a major role in these binary systems, supporting in particular a correlation between geometric effects and slower crystallization kinetics.