Abstract
Tackling the low-temperature fate of supercooled liquids is challenging because of the immense time scales involved, which prevent equilibration and lead to the operational glass transition. Relating glassy behavior to an underlying, thermodynamic phase transition is a long-standing open question in condensed matter physics. Like experiments, computer simulations are limited by the small time window over which a liquid can be equilibrated. Here, we address the challenge of low-temperature equilibration using trajectory sampling in a system undergoing a nonequilibrium phase transition. This transition occurs in trajectory space between the normal supercooled liquid and a glassy state rich in low-energy geometric motifs. Our results indicate that this transition might become accessible in equilibrium configurational space at a temperature close to the so-called Kauzmann temperature, and they provide a possible route to unify dynamical and thermodynamical theories of the glass transition.
- Received 22 March 2016
DOI:https://doi.org/10.1103/PhysRevX.7.031028
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Glass is representative of modern society: Glass windows isolate the buildings of our cities, glasses sharpen our vision, and common glass-based objects such as bowls are part of our everyday experience. However, it is challenging to appreciate what glass truly is. Water undergoes a phase change upon freezing from a disordered liquid to ordered crystal, but there is no consensus as to whether a similar phase change occurs for glasses from a liquid phase to a so-called “ideal glass phase.” Here, we develop a novel computational method for generating atomic arrangements in a glassy material and provide evidence in support of a true phase change in glass.
Gaining a better understanding of glasses is complex because low-temperature equilibrium states are hard to access, both in experiments and in computer simulations. The problem in identifying any phase change is that the constituent atoms move so slowly that it is hard to tell if they remain on their sites indefinitely as in a crystal or if they still diffuse very slowly as in a very viscous liquid. We use a novel computer simulation combining structural and dynamical information to address the problem of accessing equilibrium states at low temperature. We look for long-lived arrangements of atoms in a material resembling that are characteristic of glass and find that they look like twisted boxes (i.e., “bicapped square antiprisms”). This transition resembles freezing, but the movement of the atoms is crucial: The material remains amorphous but solid, like a glass, and flow is arrested.
We expect that our theoretical findings can be verified experimentally using colloids or granules, leading to a better understanding of the glass state and related problems where glassy features emerge, as in soft condensed-matter physics, biophysics, and computer science.