Probing the non-Debye low-frequency excitations in glasses through random pinning

Area of Science:

• Condensed Matter Physics
• Materials Science
• Statistical Mechanics

Background:

• Understanding the vibrational properties of amorphous materials like glass is crucial.
• The low-frequency spectrum of the density of states (DOS) in glasses deviates from Debye's prediction (non-Debye behavior).
• Localized vibrational modes are key to explaining these non-Debye features.

Purpose of the Study:

• To investigate the emergence and properties of low-frequency vibrational modes in a 3D model glass former.
• To analyze how introducing pinned particles affects the density of states spectrum.
• To characterize the power-law behavior of the low-frequency tail of the DOS.

Main Methods:

• Simulated a 3D model glass former.
• Introduced a random pinning field to freeze a fraction (p) of particles, breaking translational invariance.
• Analyzed the vibrational density of states (DOS) as a function of the pinned particle fraction.

Main Results:

• Non-Debye soft localized modes progressively emerge as the fraction (p) of pinned particles increases.
• The vibrational frequencies of extended modes are shifted to higher frequencies by the pinning field.
• The low-frequency tail of the DOS exhibits power-law decay (g(ω) ~ ω^α) above a critical pinned fraction (p_c).

Conclusions:

• Pinning particles is an effective method to enhance and study non-Debye soft localized modes in glasses.
• The observed power-law behavior in the DOS indicates a transition in the vibrational spectrum.
• These findings contribute to a deeper understanding of vibrational dynamics and localization in amorphous solids.