Raman-active lattice vibrations of the commensurate superlattice in 2H-TaSe2

Raman spectra have been obtained on 2H-TaSe2 at room temperature and in the commensurate charge-density-wave, superlattice state. At low temperatures six new low frequency models are seen having symmetries consistent only with a symmetric, three-charge-density wave. A microscopic model of the lattice dynamics of this state is fitted to the four strongest new Raman lines. These are assigned to amplitude and phase modes of the charge-density wave