Reflectance spectra and electrical resistivity of (Me-2-DCNQI)(2)Li1-xCux

We systematically study transport and optical properties of charge-transfer sails, (Me(2)DCNQI)(2)Li1-xCux (0 less than or equal to x less than or equ al to 1). The temperature dependence of electrical resistivity exhibits sem iconducting behavior at x = 0, a metal-semiconductor transition for 0.08 le ss than or equal to x less than or equal to 0.20, and metallic behavior dow n to 4.2K for x greater than or equal to 0.39. A semiconductor-semiconducto r transition is observed around 60K for x less than or equal to 0.14. The r eflectance spectra at room temperature reveal tno optical excitations in th e infrared region. The first excitation appears in salts with x not equal 0 far below 650 cm(-1) The second excitation is the so-called mid-infrared b and, which appears around 3000 cm(-1) for 0 less than or equal to x less th an or equal to 0.14, and shifts downward for x greater than or equal to 0.1 7. We propose a hypothesis which provides an explanation both for the metal lic conduction and for the mid-infrared band in a one-dimensional conductor having a quarter-filled band.