Raman scattering of light from a charge-density-wave (CDW) phonon in an anisotropic CDW superconductor

The probability of Raman scattering of light by a charge-density-wave (CDW) phonon is calculated for a model anisotropic system which exhibits coexistent CDW and superconducting characteristics. It is pointed out that in such a system both ordinary electron-phonon interactions and the modified Balseiro-Falicov interaction contribute to the Raman activity of the CDW phonon. The Raman spectrum obtained has features qualitatively similar to that of the renormalized spectral function of the CDW phonon previously discussed. However, the inclusion of the electron-photon vertices may considerably enhance the weight of the superconducting gap peak relative to the CDW amplitude mode. The polarizations of the incident and scattered light enter the expressions of the scattering probability, thus giving a natural explanation for the intensity difference of the gap peaks in the A and E modes observed in experiments by Sooryakumar and Klein on 2H-${\mathrm{NbSe}}_2$.