Electronic states studies of alkali-metal-doped C60 superconductors by nuclear magnetic resonance

Abstract
The density of states at the Fermi level [N(EF)] of alkali‐metal‐doped C60 superconductors having a wide range of Tc from Na2Rb1C60 (Tc=3.5 K) to Rb1Cs2C60 (Tc=33 K) is systematically studied using spin‐lattice relaxation times (T1) by NMR spectroscopy. The obtained N(EF) values suggest that the phonon modes associated with superconductivity are high and that the electron‐phonon coupling constant is responsible for the large decrease in Tc in the small lattice parameter region.