Raman scattering in organic conductors (DMe-DCNQI)2Cu

Abstract Raman scattering was measured in an organic conductor (DMe-DCNQI- h ) 2 Cu and the deuterated salts in order to study a metal-insulator transition. A new broad peak originating from the intramolecular vibrations of DCNQI molecule appeared at about 1380 cm −1 in the insulating phase of the − d 2 and − d 2 salts. Large frequency shifts and drastic sharpenings of the low-frequency phonon peaks were observed only in these salts when the temperature was decreased. This behavior can be interpreted in terms of the order-disorder effect of Cu ions in the mixed-valence state.