Phonons in stringlet-land and the boson peak

Abstract

Solid materials that deviate from the harmonic crystal paradigm exhibit characteristic anomalies in the specific heat and vibrational density of states (VDOS) with respect to Debye's theory predictions. The boson peak (BP), a low-frequency excess in the VDOS over Debye law $g(\omega )\propto {\omega }^2$, is certainly the most famous among them; nevertheless, its origin is still subject of fierce debate. Recent simulation works provided strong evidence that localized one-dimensional string-like excitations (stringlets) might be the microscopic origin of the BP. In this work, we study the dynamics of acoustic phonons interacting with a bath of vibrating 1D stringlets with exponentially distributed size, as observed in simulations. We show that stringlets strongly renormalize the phonon propagator and naturally induce a BP anomaly in the vibrational density of states, corresponding to the emergence of a dispersionless BP flat mode. Additionally, phonon-stringlet interactions produce a strong enhancement of sound attenuation and a dip in the speed of sound near the BP frequency, consistent with experimental and simulation data. The qualitative trends of the BP frequency and intensity are predicted within the model and shown to be in good agreement with previous observations. In summary, our results substantiate with a simple theoretical model the recent simulation results by Hu and Tanaka claiming the origin of the BP from stringlet dynamics.

v2: matching the published version in Journal of Physics: Condensed Matter

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Cited by in corpus (5)

• Dispersionless Flat Mode and Vibrational Anomaly in Active Brownian Vibrators Induced by String-like Dynamical Defects
• Revealing the Geometrical and Vibrational Properties of the Defects Driving the Boson Peak
• Impact of elastic inhomogeneity on collective dynamical properties investigated by field theoretical description in real space
• The anomalous density of states and quasi-localized vibration through homogeneous thermalization of an inhomogeneous elastic system
• Resonant Coupling and the Non-Phononic Flat Band in Amorphous Solids