Competition between energy- and entropy-driven activation in glasses.

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Materials Science

Background:

• Glasses exhibit complex dynamics, particularly their slowdown, which is not fully explained by traditional models.
• Existing theories often focus on energy barrier hopping as the primary mechanism for activation.

Purpose of the Study:

• To clarify the existence and interplay of two distinct activated dynamics in simplified glass models.
• To investigate the conditions under which one dynamic mechanism dominates over the other.
• To reconcile different theoretical pictures of glass slowdown.

Main Methods:

• Analysis of simplified models of glasses.
• Identification and characterization of two coexisting activated dynamics: energy barrier hopping and entropic activation.
• Investigation of the dependence of dynamic dominance on temperature and density of states.

Main Results:

• Two coexisting activated dynamics were identified: energy barrier hopping and entropic activation.
• Entropic activation, driven by phase space constraints, can dominate over energy barrier hopping.
• The dominance of each mechanism depends on temperature and the shape of the density of states.
• A phase transition between the two activation mechanisms can occur at low temperatures.

Conclusions:

• The findings provide a unified scenario harmonizing facilitation and thermodynamic descriptions of glass slowdown.
• Entropic activation offers a new perspective on the factors governing the dynamics of glassy systems.
• Understanding these distinct dynamics is crucial for predicting and controlling glass behavior.