title: Metal-insulator transitions: influence of lattice structure, jahn-teller effect, and Hund's rule coupling
abstract: We study the influence of the lattice structure, the Jahn-Teller effect, and the Hund's rule coupling on a metal-insulator transition in A(n)C60 (A = K,Rb). The difference in the lattice structure favors A3C60 (fcc) being a metal and A4C60 (bct) being an insulator, and the coupling to H(g) Jahn-Teller phonons favors A4C60 being nonmagnetic. The coupling to H(g) ( A(g)) phonons decreases (increases) the value U(c) of the Coulomb integral at which the metal-insulator transition occurs. There is an important partial cancellation between the Jahn-Teller effect and the Hund's rule coupling.
authors.affiliation: Max-Planck-Institut fur Festkorperforschung, D-70506 Stuttgart, Germany.
authors.initials: JE
authors.lastname: Han
authors.initials: E
authors.lastname: Koch
authors.initials: O
authors.lastname: Gunnarsson