Organic Conductors: Evidence for Correlation Effects in Infrared Properties

The infrared conductivities of four organic conductors with partially filled one-electron bands are compared. The behavior ranges from near Drude type in the best metal to semiconductorlike in the moderate conductor. Electron-molecular-vibration coupling effects of varying degree are seen in all materials. It is suggested that the combined effect of electron-electron interaction and electron-phonon interaction in producing $4k_{\mathrm{F}}$ charge-density waves is essential for interpreting the results.