Glasses and metastability: large deviations of dynamical observables in experiments and simulations

When glass-forming liquids are rapidly cooled, their dynamics changes dramatically: the particle motion becomes heterogenous and cooperative, and the relaxation times rapidly exceed any human time-scale.Whether a genuine... [ view full abstract ]

When glass-forming liquids are rapidly cooled, their dynamics changes dramatically: the particle motion becomes heterogenous and cooperative, and the relaxation times rapidly exceed any human time-scale.Whether a genuine thermodynamic phase transition lies behind such a phenomenology is unknown.However, when computing time-integrated quantities, a measurable, well-defined transition in the space of multiple realisations of the liquid dynamics (trajectories) naturally emerges. Employing the concepts of locally favoured structures and large deviations of time-integrated observables, we show that such dynamical phase transition corresponds to the existence of two (stable and metastable) liquid states of a model atomistic glass-former, separated by a free energy barrier that vanishes as we lower the temperature [1]. Extrapolation indicates a finite, non-zero temperature at which the metastable, low-energy, structure-rich phase would become stable. To complement this scenario, a first experimental evidence of the same dynamical transition is also provided in a supersaturated mixture of polydisperse colloidal hard-spheres [2], suggesting that the phenomenology is common to glass-formers of different interactions and fragilities.

[1] F. Turci, C. P. Royall and T. Speck. Under review at PRX. arXiv:1603.06892

[2] R. Pinchaipat, M. Campo, F. Turci, J. Hallett, T. Speck, C. P. Royall. Under review at PRL. arXiv:1609.00327