Raman-Active Lattice Vibrations of the Commensurate Superlattic in2H−TaSe2

Raman spectra have been obtained on $2H-\mathrm{Ta}{\mathrm{Se}}_2$ at room temperature and in the commensurate charge-density-wave, superlattice state. At low temperatures six new low frequency modes 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.