It is well known that amorphous solids display a phonon spectrum where the Debye ∼ω2 law at low frequency melds into an anomalous excess-mode peak (the boson peak) before entering a quasilocalized regime at higher frequencies dominated by scattering. The microscopic origin of the boson peak has remained elusive despite various attempts to put it in a clear connection with structural disorder at the atomic/molecular level. Using numerical calculations on model systems, we show that the microscopic origin of the boson peak is directly controlled by the local breaking of center-inversion symmetry. In particular, we find that both the boson peak and the nonaffine softening of the material display a strong correlation with a new order parameter describing the local inversion symmetry of the lattice. The standard bond-orientational order parameter, instead, is shown to be inadequate and cannot explain the boson peak in randomly-cut crystals with perfect bond-orientational order. Our results bring a unifying understanding of the boson peak anomaly for model glasses and defective crystals in terms of a universal local symmetry-breaking principle of the lattice.

Local inversion-symmetry breaking controls the boson peak in glasses and crystals / R. Milkus, A. Zaccone. - In: PHYSICAL REVIEW. B. - ISSN 2469-9950. - 93:9(2016 Mar 21), pp. 094204.094204-1-094204.094204-10. [10.1103/PhysRevB.93.094204]

Local inversion-symmetry breaking controls the boson peak in glasses and crystals

A. Zaccone
2016

Abstract

It is well known that amorphous solids display a phonon spectrum where the Debye ∼ω2 law at low frequency melds into an anomalous excess-mode peak (the boson peak) before entering a quasilocalized regime at higher frequencies dominated by scattering. The microscopic origin of the boson peak has remained elusive despite various attempts to put it in a clear connection with structural disorder at the atomic/molecular level. Using numerical calculations on model systems, we show that the microscopic origin of the boson peak is directly controlled by the local breaking of center-inversion symmetry. In particular, we find that both the boson peak and the nonaffine softening of the material display a strong correlation with a new order parameter describing the local inversion symmetry of the lattice. The standard bond-orientational order parameter, instead, is shown to be inadequate and cannot explain the boson peak in randomly-cut crystals with perfect bond-orientational order. Our results bring a unifying understanding of the boson peak anomaly for model glasses and defective crystals in terms of a universal local symmetry-breaking principle of the lattice.
Settore FIS/03 - Fisica della Materia
Settore FIS/02 - Fisica Teorica, Modelli e Metodi Matematici
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/828859
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