Emergence of two-level systems in glass formers: a kinetic Monte Carlo study

TL;DR

This study uses a lattice model and kinetic Monte Carlo simulations to explain how two-level systems emerge in glass formers, linking microscopic dynamics to macroscopic thermal properties across temperature regimes.

Contribution

It introduces a lattice-based model that reproduces the heat capacity behavior and elucidates the microscopic origin of two-level systems in glasses.

Findings

Reproduces linear heat capacity-temperature relation at low temperatures

Shows two-level systems arise from void localization in the model

Provides a unified microscopic framework for glass dynamics

Abstract

Using a distinguishable-particle lattice model based on void-induced dynamics, we successfully reproduce the well-known linear relation between heat capacity and temperature at very low temperatures. The heat capacity is dominated by two-level systems formed due to the strong localization of voids to two neighboring sites, and can be exactly calculated in the limit of ultrastable glasses. Similar but weaker localization at higher temperatures accounts for the glass transition. The result supports the conventional two-level tunneling picture by revealing how two-level systems emerge from random particle interactions, which also cause the glass transition. Our approach provides a unified framework for relating microscopic dynamics of glasses at room and cryogenic temperatures.