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

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 S_K = 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.