Raman scattering in metallic Si and Ge up to 50 GPa

Abstract

Optical phonons in metallic high-pressure phases of Si and Ge were studied up to 50 GPa by Raman scattering. Two Raman bands (LO, TO) were observed in the \ensuremath{\beta}-tin phase, one of which (LO) becomes soft on approaching the transition to primitive hexagonal. For hcp-Si there is one Raman-active mode (TO), and an additional mode is observed in the stability field of Si-VI. The available theoretical results agree within (10--20)% with the experimental results.