TRANSVERSE ACOUSTIC PHONONS OF GERMANIUM UP TO 9.7 GPA BY NEUTRON INELASTIC-SCATTERING

Recent progress in high pressure neutron techniques now permits the me asurement of the phonon dispersion curves of germanium at pressures up to 10 GPa. Inelastic neutron scattering measurements on 25 mm(3) sing le crystals have been performed for the first time up to 9.7 GPa, that is close to its pressure-induced phase transition. Frequency Variatio ns of the phonon modes were measured along the [100], [110], and [III] directions and are shown to have a nonlinear volume dependence for al l wavevectors. These results are compared with published data on the b ehaviour of TA modes in tetrahedral semiconductors and with recent cal culations using the density functional formalism. The agreement betwee n experiment and theory is remarkable and underlines the potential of ab initio calculations for accurately describing the lattice dynamics of semiconductors at variable density.