Dominance of the spin-dipolar NMR relaxation mechanism in Fullerene superconductors

V.P. Antropov, I.I. Mazin, O.K. Andersen, I. Liechtenstein, and O. Jepsen
Max-Planck-Institut für Festkörperforschung, Stuttgart

We have performed ab initio calculations for the NMR relaxation rate in doped fullerenes and find that the spin-dipolar relaxation mechanism dominates the orbital and Fermi-contact mechanisms. The reason is that the states at the Fermi level are pp pi-like so that the carbon orbitals have almost exclusively radial p character. With the values 7.2 and 8.1 states/(eV spin molecule) for the bare density of states at the Fermi level for, respectively, K3C60 and Rb3C60, plus the ab inition value 1.7 eV spin C atom for the effective Stoner exchange parameter, godd agreement is obtained with the experimental relaxation rates.

Phys. Rev. B 47, 12373 (1993).