Vibrational behaviour of a realistic amorphous-silicon model

TL;DR

This study investigates the vibrational properties of a realistic amorphous silicon model, analyzing dynamical structure factors and their damping behaviors, revealing different scaling laws for longitudinal and transverse vibrations.

Contribution

It provides detailed analysis of vibrational damping in amorphous silicon, including the scaling of damping widths and the absence of expected quartic behavior.

Findings

Longitudinal damping width scales as k^2 for certain wavevectors.

Transverse damping width scales approximately as k^2.5.

No evidence of k^4 damping behavior was observed.

Abstract

The vibrational properties of a high-quality realistic model of amorphous silicon are examined. The longitudinal and transverse dynamical structure factors are calculated, and fitted to a damped harmonic oscillator (DHO) function. The width $\Gamma$ of the best-fit DHO to the longitudinal dynamical structure factor scales approximately as $k^{2}$ for wavevectors $k\lesssim0.55\textrm{\AA}^{-1}$, which is above the Ioffe-Regel crossover frequency separating the propagating and diffusing regimes, occurring at $k=0.38\pm0.03\textrm{\AA}^{-1}$. Using the DHO function as a fitting function for the transverse dynamical structure factor (without theoretical justification), gives a dependence of $\Gamma\propto k^{\alpha}$ with $\alpha\sim2.5$ for wavevectors $k\lesssim0.7\textrm{\AA}^{-1}$. There was no evidence for $\Gamma\propto k^{4}$ behaviour for either polarization.