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

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 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. Our approach provides an unified framework for relating microscopic dynamics of glasses at room and cryogenic temperatures.