Observation of crystallization slowdown in supercooled parahydrogen and orthodeuterium quantum liquid mixtures

We report a quantitative experimental study of the crystallization kinetics of supercooled quantum liquid mixtures of parahydrogen (pH2) and orthodeuterium (oD2) by high spatial resolution Raman spectroscopy of liquid microjets. We show that in a wide range of compositions the crystallization rate of the isotopic mixtures is significantly reduced with respect to that of the pure substances. To clarify this behavior we have performed path-integral simulations of the nonequilibrium pH2-oD2 liquid mixtures, revealing that differences in quantum delocalization between the two isotopic species translate into different effective particle sizes. Our results provide experimental evidence for crystallization slowdown of quantum origin, offering a benchmark for theoretical studies of quantum behavior in supercooled liquids.