Metallic and insulating states in two-dimensional C60-polymers

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