Infrared Reflectance Spectra of (Me₂DCNQI-d₇)₂Cu

Abstract

The temperature dependence of polarized infrared reflectance spectra was investigated on the single crystal of (Me₂DCNQI-d₇)₂Cu whose electrical resistivity was continuously monitored by the four-probe method. Above 77, K, the resistivity decreases on lowering the temperature, and the reflectance spectra exhibit Drude-like dispersion for both polarizations parallel and perpendicular to the crystallographic c-axis. Between 77, K and 75, K, the resistivity increases more than 10⁶ times that of 77, K, and the reflectance spectra exhibit drastic change suggesting dimensionality crossover from a three-dimensional conductor into a one-dimensional insulator. Based on the reflectivity data it was concluded that the metal-insulator transition in this salt is accompanied by discontinuous formation of CDW.