Metal-insulator transitions: influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling.

Han J.E., Koch E., Gunnarsson O.

Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany

We study the influence of the lattice structure, the Jahn-Teller effect, and the Hund's rule coupling on a metal-insulator transition in AnC60 (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 Hg Jahn-Teller phonons favors A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases) the value Uc 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. 

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Physical Review Letters, 84 1276-9, 2000.

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