Electronic properties of normal and superconducting alkali fullerides probed byC13nuclear magnetic resonance

We report the results of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR measurements on ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3$ ${\mathrm{C}}_{60}$ in the normal and superconducting states. Electronic densities of states at the Fermi energy in the normal-state and energy gaps in the superconducting state are estimated from spin-lattice-relaxation data. Implications of the relaxation and spectral data for the electronic properties of these materials are discussed.