EPR test of the resonating-valence-bond theory of superconductivity in C60Kn

EPR experiments on powder samples of C60Kn are presented. The results contradict the basic assumption of a negative Hubbard U, which has been used to explain the superconductivity in fullerenes. The apparent orbital nondegeneracy of the observed state is explained in terms of a generalized dynamic Jahn-Teller effect. © 1992 The American Physical Society.