Dynamic Heterogeneity in Crossover Spin Facilitated Model of Supercooled Liquid and Fractional Stokes-Einstein Relation

TL;DR

This paper explores the dynamic heterogeneity and fractional Stokes-Einstein relation in a kinetically constrained model that interpolates between fragile and strong glass-forming liquids, revealing a fragile-to-strong transition and associated length scales.

Contribution

It introduces a new interpolating model that captures the fragile-to-strong transition and analyzes the fractional Stokes-Einstein relation and dynamic length scales in this context.

Findings

Observation of a smooth fragile-to-strong transition in relaxation time and diffusion constant.

Constant power law exponent for the fractional Stokes-Einstein relation across temperatures.

Identification of a crossover relation between relaxation time and dynamic length scale.

Abstract

Kinetically constrained models (KCMs) have gained much interest as models that assign the origins of interesting dynamic properties of supercooled liquids to dynamical facilitation mechanisms that have been revealed in many expreiments and numerical simulations. In this work, we investigate the dynamic heterogeneity in the fragile-to-strong liquid via Monte Carlo method using the model that linearly interpolates between the strong-liquid like behavior and the fragile-liquid like behavior by an asymmetry parameter b. When the asymmetry parameter is sufficiently small, smooth fragile-to-strong transition is observed both in the relaxation time and the diffusion constant. Using these physical quantities, we investigate fractional Stokes-Einstein relations observed in this model. When b is fixed, the system shows constant power law exponent under the temperature change, and the exponent has the value between that of the FA model and the East model. Furthermore, we investigate the dynamic length scale of our systems and also find the crossover relation between the relaxation time. We ascribe the competition between energetically favored symmetric relaxation mechanism and entropically favored asymmetric relaxation mechanism to the fragile-to-strong crossover behavior.