A characteristic energy scale in glasses

Area of Science:

• Condensed Matter Physics
• Materials Science
• Statistical Mechanics

Background:

• Glassy materials exhibit intrinsic structural disorder, leading to broad distributions of microscopic properties.
• Macroscopic responses of glasses are often explained by a characteristic energy scale, but this has not been robustly identified.
• Soft quasilocalized excitations are known to play a critical role in glass dynamics.

Purpose of the Study:

• To propose and identify a characteristic energy scale that governs the macroscopic response of glassy materials.
• To investigate the properties and behavior of this energy scale in relation to the glass transition.
• To establish connections between this energy scale, structural disorder, and material dynamics.

Main Methods:

• Calculating the bulk average of the glass response to a localized force dipole.
• Analyzing the inherent structures of equilibrium supercooled states near the glass transition temperature (Tg).
• Comparing the energy scale's variation with annealing and system size to the energy of the softest non-phononic vibrational mode.

Main Results:

• A characteristic glassy energy scale was defined and found to increase dramatically as the glass transition temperature (Tg) is approached.
• This energy scale's variation mirrors that of the softest non-phononic vibrational mode, linking rare fluctuations to bulk responses.
• The energy scale shows significant dependence on spatial dimensionality and system size, with implications for 2D glasses.

Conclusions:

• The proposed characteristic energy scale provides a robust metric for understanding glass behavior and dynamics.
• The findings challenge the notion of minute structural variations in supercooled liquids near Tg.
• A growing lengthscale associated with this energy scale was identified, potentially explaining the slowing down of dynamics near Tg.