d Orbital doping into pi charge-ordered molecular insulator

A quasi-one-dimensional pi-electron charge-ordered insulator, (DI-DCNQI)2Ag, is metallized by Cu doping into the Ag sites. It is found that with doping the charge gap is diminished and then disorder-induced insulating nature comes up, eventually followed by transition or crossover to a pi-d networked metal. The profile of the charge-gap collapse is consistent with the prediction of the theory highlighting the interplay between electron correlation and disorder. The present doping method is regarded as doping of d orbital, which is different from the conventional charge and/or spin doping developed in cuprates and manganites.