Low-frequency vibrational modes of stable glasses

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Materials Science

Background:

• The vibrational density of states (D(ω)) in glasses influences their low-temperature properties.
• Previous simulations focused on poorly annealed glasses, limiting experimental relevance.
• Understanding D(ω) in stable glasses is crucial for materials design.

Purpose of the Study:

• To investigate the vibrational density of states (D(ω)) in glasses across a range of kinetic stabilities, from poorly annealed to ultrastable.
• To identify and characterize low-frequency vibrational modes in these glasses.
• To establish a link between glass stability and its vibrational characteristics.

Main Methods:

• Numerical simulations of glasses at zero temperature.
• Analysis of the vibrational density of states (D(ω)).
• Characterization of extended and quasi-localized vibrational modes.

Main Results:

• The low-frequency D(ω) consistently splits into extended and quasi-localized modes across all glass stabilities.
• Extended modes show Debye behavior (D_ex(ω) ~ ω²) at low frequencies, correlating with the boson peak.
• Quasi-localized modes follow a D_loc(ω) ~ ω⁴ relationship, becoming sparser and more localized with increasing glass stability.

Conclusions:

• This work provides the first numerical observation of quasi-localized modes in experimentally relevant glasses.
• A direct correlation between glass kinetic stability and the nature of its soft vibrational modes is established.
• Findings offer insights into the relationship between structure, dynamics, and properties of glasses.