Boson-peak vibrational modes in glasses feature hybridized phononic and quasilocalized excitations

Abstract

A hallmark of structural glasses and other disordered solids is the emergence of excess low-frequency vibrations, on top of the Debye spectrum $D_{\mathrm{Debye}}(\omega )$ of phonons ($\omega$ denotes the vibrational frequency), which exist in any solid whose Hamiltonian is translationally invariant. These excess vibrations -- a signature of which is a THz peak in the reduced density of states $D(\omega )/D_{\mathrm{Debye}}(\omega )$, known as the boson peak -- have resisted a complete theoretical understanding for decades. Here, we provide direct numerical evidence that vibrations near the boson peak consist of hybridizations of phonons with many quasilocalized excitations, the latter were recently shown to generically populate the low-frequency tail of the vibrational spectra of structural glasses quenched from a melt and of disordered crystals. Our results suggest that quasilocalized excitations exist up to and in the vicinity of the boson-peak frequency, and hence constitute fundamental building blocks of the excess vibrational modes in glasses.

9 pages, 6 figures. v2: additional analysis + 2 new figures

References in corpus (5)

• Energy transport in jammed sphere packings
• Nonlinear modes disentangle glassy and Goldstone modes in structural glasses
• The boson peak in the vibrational spectra of glasses
• Disordered crystals reveal soft quasilocalized glassy excitations
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• Testing the Heterogeneous-Elasticity Theory for low-energy excitations in structural glasses
• Revealing the Geometrical and Vibrational Properties of the Defects Driving the Boson Peak
• Enumerating low-frequency nonphononic vibrations in computer glasses
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• Resonant Coupling and the Non-Phononic Flat Band in Amorphous Solids
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