The anomalous density of states and quasi-localized vibration through homogeneous thermalization of an inhomogeneous elastic system

TL;DR

This paper explains the anomalous low-frequency vibrational density of states in amorphous solids as a consequence of homogeneous thermalization under quasi-equilibrium conditions, linking inhomogeneity to vibrational properties.

Contribution

It provides an analytical derivation showing how quasi-equilibrium conditions lead to the $ ext{VDOS} \, \propto \, \omega^4$ behavior in inhomogeneous elastic systems, connecting microscopic inhomogeneity to macroscopic vibrational anomalies.

Findings

Derivation of $D(\omega) \propto \omega^4$ behavior under quasi-equilibrium.

Identification of a crossover to Debye's law $D(\omega) \propto \omega^2$ at high frequencies.

Agreement with recent particle-level investigations on amorphous solids.

Abstract

Amorphous solids are dynamically inhomogeneous due to in lack of translational symmetry and hence exhibit vibrational properties different from crystalline solids with anomalous low frequency vibrational density of states (VDOS) and related low temperature thermal properties. However, an interpretation of their origin from basic physical laws is still needed compared with rapidly progressed particle level investigations. In this work, we start with the quasi-equilibrium condition, which requires elastic potential energy to be homogeneously distributed even in an inhomogeneous elastic solid over long time observation. Analytical result shows that the anomalous low frequency VDOS behavior $D(\omega) \propto \omega^4$ can be obtained when the quasi-equilibrium condition is satisfied on an inhomogeneous elastic system. Under high frequency after a crossover depending on the length scale of inhomogeneity, the power law of VDOS is changed to square $D(\omega) \propto \omega^2$ which is Debye's law for crystalline solids. These features agree with recent particle level investigations. Our work suggest that the universal low frequency anomaly of amorphous solids can be considered as a result of homogeneous thermalization.