Analysis of the 13C Knight shift and spin-lattice relaxation in A3C60 (A = Rb or K)

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Abstract
The density of states is derived from 13C Knight shift data to 8.6 eV−1 spin−1 C60 −1 for Rb3C60 and 6.8 eV−1 spin−1 C60 −1 for K3C60 at room temperature. It is shown that the simple Korringa relation does not hold for A3C60, that is density-of-states information cannot be obtained from T1 data. A modified Korringa relation must be applied instead by including a Korringa scaling factor S K, which is obtained as SK = 2.5 (Rb3C60) and 2.7 (K3C60) at room temperature. The anisotropic hyperfine interaction which is dominant here has been included. Non-exponential relaxation is predicted to occur from this anisotropy. The deviation from the Korringa value (S K = 1.0) may indicate appreciable electron-electron correlation or charge-density wave dynamics in A3C60.