Raman Spectroscopy of Soft Modes at the Charge-Density-Wave Phase Transition in2HNbSe2

Abstract
The Raman spectra of the layer-structure compounds 2HNbSe2 and 2HTaSe2 have been measured between 2 and 300 K. A low-energy peak in the Raman spectrum is found to soften at the charge-density-wave phase transition. This peak is attributed to the charge-density-wave amplitude mode. The intensity and energy of this soft mode have been successfully compared with mean-field treatments of the charge-density-wave phase transition.