Y. Lin et Je. Eldridge, FLUCTUATION EFFECTS ON THE RAMAN-SCATTERING FROM THE CHARGE-DENSITY-WAVE SYSTEM TTF-TCNQ, Physical review. B, Condensed matter, 58(7), 1998, pp. 3477-3481
The resonant Raman spectrum of TTF-TCNQ has been measured from room te
mperature to IO K, using a Fourier Raman spectrometer. Only features d
ue to the TCNQ molecule are observed. New Raman lines appear at temper
atures below 150 K as the fluctuating charge-density wave (CDW) occurs
. The intensity of the new Raman lines increases with decreasing tempe
rature. In addition to the Raman allowed modes, we observe numerous Li
nes originating from the usually infrared-active-only modes, which bec
ome Raman active via the Frohlich interaction in the fluctuating and s
tatic CDW phases. The appearance of the strong out-of-plane intramolec
ular B-3u vibrational modes of TCNQ confirms an earlier x-ray study th
at found that the CDW on the TCNQ chain involved such an out-of-plane
distortion of the TCNQ molecule. The condensation of the longitudinal
acoustic phonon is also observed in the Raman spectrum.