Mott transition and superconductivity in alkali-doped fullerides

O. Gunnarsson(1), E. Koch (1,2) and R.M. Martin(2)
(1) Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany (2) Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Il 61801

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.

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Electronic Properties of novel Materials - Progress in molecular nanostructures, Eds. H. Kuzmany, J. Fink, M. Mehring, and S. Roth, AIP Conference Proceedings 442, (Woodbury, New York, 1998), p. 287.