Vibrational density of states of amorphous solids with long-ranged power-law correlated disorder in elasticity

TL;DR

This paper develops a theoretical framework to predict the vibrational density of states in amorphous solids with power-law correlated disorder, revealing the origin of the boson peak and phonon attenuation features.

Contribution

It introduces the first prediction of a boson peak in systems with power-law correlated elastic disorder, including analytical and numerical results.

Findings

Predicts a logarithmic enhancement of phonon attenuation.

Identifies a $ u^4$ scaling law in the low-frequency DOS.

Derives the form of the boson peak and its dependence on disorder strength.

Abstract

A theory of vibrational excitations based on power-law spatial correlations in the elastic constants (or equivalently in the internal stress) is derived, in order to determine the vibrational density of states $D(\omega)$ of disordered solids. The results provide the first prediction of a boson peak in amorphous materials where spatial correlations in the internal stresses (or elastic constants) are of power-law form, as is often the case in experimental systems, leading to logarithmic enhancement of (Rayleigh) phonon attenuation. A logarithmic correction of the form $\sim -\omega^{2}\ln\omega$ is predicted to occur in the plot of the reduced excess DOS for frequencies around the boson peak in 3D. Moreover, the theory provides scaling laws of the density of states in the low-frequency region, including a $\sim\omega^{4}$ regime in 3D, and provides information about how the boson peak intensity depends on the strength of power-law decay of fluctuations in elastic constants or internal stress. Analytical expressions are also derived for the dynamic structure factor for longitudinal excitations, which include a logarithmic correction factor, and numerical calculations are presented supporting the assumptions used in the theory.