Neutron scattering investigations of the boson peak

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(2)S (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 SiO2, B2O3, 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.