METALLIC BEHAVIOR INDUCED BY LI-DOPING IN DCNOI-CU SYSTEM

Li-doping has shown drastic effect on temperature-dependence of resistivity in the mixed valence Cu salt (DBr-DCNQI)2Cu. (DBr-DCNQI)2Li is isostructural with (DBr-DCNQI)2Cu and is a semiconductor. The pure Cu salt exhibits first-order metal-insulator transition at 160 K. A small amount of Li+ lowered the transition temperature. In the course of further increase in the Li concentration, a 'reentrance'' of the metallic state was observed at low temperatures. In this region, both of non-metallic and low-temperature metallic states were accompanied by a three-fold lattice distortion along the crystallographic c axis. While the Li-doping changes the formal charge of the DBr-DCNQI molecule continuously, the observed period of the superstructure was always constant. The electronic state at this ''reentrance'' region is discussed in the light of heavy electron. Similar stable metallic state induced by the Li-doping was observed in (DMe-DCNQI-d7)2Cu1-xLix.