STRONGLY CORRELATED ELECTRONS IN MIXED-VALENCE CONDUCTORS DCNQI-CU SALTS

Organic conductors, DCNQI-Cu salts, with a mixed valence Cu+4/3 on the average has been studied theoretically by applying the slave-boson method to the strongly correlated systems which consist of pi-electrons of DCNQI molecule and d-electrons of Cu atoms. The ground state is calculated by use of the 1/N(sigma) expansion method which treats the local constraint strictly. It is shown that the electron mass around the Fermi surface is enhanced in the presence of the charge density with the three-fold periodicity.