J.E. Han and O. Gunnarsson
*
Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
*

We consider a model which includes the electron-phonon coupling to Ag or Jahn-Teller Hg phonons, the Coulomb interaction U and an exchange integral K. We study the metal-insulator transition for the integer fillings n=3 and 4. We find that the coupling to Ag phonons increases the critical value Uc where the transition takes place, while the coupling to Hg phonons decreases Uc. Without electron-phonon coupling the Hund's rule coupling also decreases Uc. There is, however, an interesting competition between the Hund's rule coupling and the Jahn-Teller effect. Thus the reduction of Uc due to the Hg phonons becomes smaller when the Hund's rule coupling is turned on. The implications of this is discussed in the context of AnC60.

A postscript file is available at this http URL

Physica B **292**, 196 (2000).

Max-Planck Institut für Festkörperforschung

Postfach 800 665 D-70506 Stuttgart