Infrared reflectance spectra of DCNQI salts

Temperature dependence of polarized infrared reflectance spectra were measured for single crystals of (Me2DCNQI-d7)2Cu under the stress reduced as weak as possible. The reflectance spectra exhibit drastic change suggesting a crossover from a three-dimensional conductor into a one-dimensional insulator, while this feature smears in the stressed sample. Based on the reflectivity data, it is concluded that the metal-insulator transition is accompanied by discontinuous formation of CDW.