Theory of metal-insulator transition in (DCNQI)/sup2/Cu

Summary form only given. The metal-insulator transition of (DCNQI)/sub 2/Cu has various unique features; 1) The transition is of first order with very large hysterisis. 2) In the insulating phase there exists threefold superlattice distortions. 3) Although the temperature independent Pauli like spin susceptibility is observed in the metallic state, the localized spins are created in the insulating phase. 4) The average valence of Cu is 4/3 in both metallic and insulating state. 5) A reentrant metallic state is stabilized for some particular range of effective internal pressure. All of above mentioned experimental facts of this /spl pi/ - d system I)-4) are explained as a unique situation of the Peierls transition of the /spl pi/-band with the Mott transition of the d-band, and a possible mechanism of 5) has been proposed based on the quantum tunneling of the protons.