Non-monotonic temperature evolution of dynamic correlations in glass-forming liquids

Abstract

International audienceThe viscosity of glass-forming liquids increases by many orders of magnitude if their temperature is lowered by a mere factor of 2-3. Recent studies suggest that this widespread phenomenon is accompanied by spatially heterogeneous dynamics, and a growing dynamic correlation length quantifying the extent of correlated particle motion. Here we use a novel numerical method to detect and quantify spatial correlations that reveal a surprising non-monotonic temperature evolution of spatial dynamical correlations, accompanied by a second length scale that grows monotonically and has a very different nature. Our results directly unveil a dramatic qualitative change in atomic motions near the mode-coupling crossover temperature, which involves no fitting or indirect theoretical interpretation. These findings impose severe new constraints on the theoretical description of the glass transition, and open several research perspectives, in particular for experiments, to confirm and quantify our observations in real materials

Decorrelation of the static and dynamic length scales in hard-sphere glass formers

“…The signature of a competition between different relaxation mechanisms in the same regime has been recently observed in related models [40,45] (see also Ref. [69]).…”

“…More recently, approaches that detect the growth in static correlations while staying clear of any specific proposal about local order, i.e., "order-agnostic" approaches, have been developed. Among these proposals, we note patch repetition lengths [30,31], length scales extracted from information theoretic analysis [32,33] or from finite-size studies of the configurational entropy [34], and other "point-to-set" correlation lengths [35][36][37][38][39][40].…”

“…Such a length has been called "dynamical" in Refs. [38,40], but it should be kept in mind that it is a priori different from the length characterizing the extent of the dynamical heterogeneity [47].…”

“…For the second, most data on dynamical lengths characterize the typical extent of the heterogeneous dynamics and are consistent with each other. As mentioned above, there is evidence that a "dynamical" length extracted from finite-size scaling behaves differently [40,47], but we shall here mainly focus on the lengths extracted from fourpoint space-time correlation functions.…”

Free energy cost of forming an interface between a crystal and its frozen version

“…An analogous situation corresponding to a supercooled liquid in contact with a wall consisting of particles frozen into the same amorphous structure as the liquid has been widely studied in recent years in order to investigate the relaxation dynamics of glass-forming systems [12][13][14][15][16][17][18][19]. Recently, an experimental investigation of such a system was carried out using colloidal particles [20].…”