Coulomb Suppression of NMR Coherence Peak in Fullerene Superconductors

The suppressed NMR coherence peak in the fullerene superconductors is explained in terms of the dampings induced by the Coulomb interaction between conduction electrons. The Coulomb interaction, modeled in terms of the on-site Hubbard repulsion, is incorporated into the Eliashberg theory of superconductivity with its frequency dependence considered self-consistently at all temperatures. The vertex correction is also included via the method of Nambu. The frequency dependent Coulomb interaction induces the substantial dampings in the superconducting state and, consequently, suppresses the anticipated NMR coherence peak of fullerene superconductors as found experimentally.