Neutron scattering study of the lattice dynamics of AgBr at 4.4 K

Abstract

The phonon dispersion relations of AgBr at 4.4 K have been measured in the three principal symmetry directions using the triple-axis neutron scattering technique. The data have been fitted by the extended shell model developed by Cochran et al. and the one-phonon density of states has been calculated. Near the zone boundary in the [111] direction ($L$ point), high-resolution measurements of the TA and TO phonon intensities have been carried out. The character inversion between these two modes at $L$ originally predicted by Fischer et al. is clearly evidenced from the observed intensities. The present model fit can also reproduce this character inversion. Infrared absorption and luminescence spectra of AgBr have been remeasured at 2 K with high resolution and low concentration of impurities. The observed spectral shape of the one-phonon sidebands can be successfully analyzed using the one-phonon density of states obtained at 4.4 K in the present study.