Raman spectroscopy of the charge-density-wave state in 1T- and 2H-TaSe2

The Raman spectrum of 1T-TaSe2 has been studied for 2<T<480 K. Changes in the Raman spectra have been observed which are correlated with the 473-K phase transition from the commensurate charge-density-wave (CDW) state to the incommensurate CDW state. The temperature dependence of the Raman spectra is related to changes in the magnitude of the CDW order parameter in the commensurate state. Comparison of the temperature-dependent Raman spectra of 1T- and 2H-TaSe2, suggests that the observation of multiple CDW-induced lines at energies below 100 cm-1 is partly due to the existence of secondary order parameters in the CDW state. © 1977 The American Physical Society.