Charge transfer and reentrant phenomenon in deuterated (DMe-DCNQI)2Cu

Li-doping in Cu salt of deuterated DMe-DCNQI-d7 system has shown drastic effects on physical properties. Undoped (DMe-DCNQI-d7)2Cu exhibits a first-order metal-insulator (M-I) transition at 80K, and the Li salt, which is isostructural with the Cu salt, is a one-dimensional (1D) conductor. A small amount of Li-doping suppresses the M-I transition. The M-I-M (reentrant) transition which is similar to that in selectively deuterated (DMe-DCNQI)2Cu appears in a narrow region of Li contents x. The x — T phase diagram under ambient pressure well reproduces P - T phase diagram of (DMe-DCNQI)2Cu system. Based on these results, an importance of the degree of charge transfer is described.