Metallic and insulating states in two-dimensional C60 polymers

Variations in the band structures of the two-dimensional C60 polymers are studied, when the π-conjugation conditions are changed. We investigate the rectangular and triangular polymers, in order to discuss metal-insulator transitions, using a semi-empirical model with Su-Schrieffer-Heeger-type electron-phonon interactions. We find that the electronic structures change among direct-gap insulators and the metal, depending on the degree of π conjugations in the rectangular polymer. The triangular polymer changes from the indirect gap insulator to the metal as the π conjugations increase. High pressure experiments could observe such pressure-induced metal-insulator transitions.