Max-Planck-Institut für Festkörperforschung, D-70506 Stuttgart, Germany;
Department of Physics, University of Illinois, Urbana, Illinois 6180

We study the effects of deviations from cubic symmetry on superconductivity and on Mott transitions by comparing A₃C₆₀ and NH₃K₃C₆₀. The reduced frustration in NH₃K₃C₆₀ favours a Mott transition at a lower ratio U/W, where U is the Coulomb repulsion of two electrons on the same molecule and W is the width of the t_1u band. The closeness of NH₃K₃C₆₀ to a Mott transition may influence the superconductivity negatively, due to an inefficient screening of the Coulomb repulsion.
 
 

in: Electronic Properties of novel Materials. Eds. H. Kuzmany, J. Fink, M. Mehring, S. Roth. Woodbury, NY: AIP, 287-291 (CP442) (1998 Kirchberg Winterschool Proc.).