Neutron scattering investigations of the boson peak

TL;DR

This paper uses inelastic neutron scattering to analyze vibrational states and eigenvectors around the boson peak in glasses, revealing insights into sound wave contributions and temperature effects.

Contribution

It introduces a method to determine eigenvectors and sound wave fractions at the boson peak using neutron scattering, with new data on various glassy materials.

Findings

Sound wave fraction at the boson peak determined for multiple glasses.

Temperature dependence of the boson peak observed in silica and glycerol.

Damping of longitudinal sound waves follows the soft potential model in silica and glycerol.

Abstract

Inelastic neutron scattering is not only capable of determining a generalized vibrational density of states around the boson peak of a glass, but can also be used to get information on the eigenvectors. The eigenvectors determine the dynamic structure factor, which is $Q^2S(Q)$ ($Q$ wavevector) for long wavelength sound waves. This enables the determination of the sound wave fraction below and at the boson peak, done for SiO$_2$, B$_2$O$_3$, polybutadiene and amorphous germanium. The temperature dependence of the boson peak in silica and glycerol is shown. X-ray Brillouin scattering data show that the damping of the longitudinal sound waves in silica and glycerol follows the soft potential model $\omega^4$ prediction in the limit of low frequency.