Local random configuration-tree theory for string repetition and facilitated dynamics of glass

TL;DR

This paper develops a microscopic theory for glassy dynamics based on void transport and micro-string motions, revealing how local configuration trees and void interactions influence particle diffusion and immobility at low temperatures.

Contribution

It introduces a novel configuration-tree framework for understanding glass dynamics, incorporating void interactions and percolation transitions in the configuration space.

Findings

Explicit expressions for diffusion coefficient and return probability.

Identification of a sequence of percolation transitions with decreasing temperature.

Good quantitative agreement with a lattice model using two adjustable parameters.

Abstract

We derive a microscopic theory of glassy dynamics based on the transport of voids by micro-string motions, each of which involves particles arranged in a line hopping simultaneously displacing one another. Disorder is modeled by a random energy landscape quenched in the configuration space of distinguishable particles, but transient in the physical space as expected for glassy fluids. We study the evolution of local regions with m coupled voids. At low temperature, energetically accessible local particle configurations can be organized into a random tree with nodes and edges denoting configurations and micro-string propagations respectively. Such trees defined in the configuration space naturally describe systems defined in two- or three-dimensional physical space. A micro-string propagation initiated by a void can facilitate similar motions by other voids via perturbing the random energy landscape, realizing path interactions between voids or equivalently string interactions. We obtain explicit expressions of the particle diffusion coefficient and a particle return probability. Under our approximation, as temperature decreases, random trees of energetically accessible configurations exhibit a sequence of percolation transitions in the configuration space, with local regions containing fewer coupled voids entering the non-percolating immobile phase first. Dynamics is dominated by coupled voids of an optimal group size, which increases as temperature decreases. Comparison with a distinguishable-particle lattice model (DPLM) of glass shows very good quantitative agreements using only two adjustable parameters related to typical energy fluctuations and the interaction range of the micro-strings.