Electronic properties of K₃C₆₀ studied by ¹³C nuclear-magnetic-resonance spectra

¹³C nuclear-magnetic-resonance (NMR) spectra are obtained to investigate the electronic properties of a superconducting fulleride K₃C₆₀. Asymmetric line shapes below 235 K are reproduced by the powder patterns of anisotropic NMR frequency shifts (K₁) of electronic single-site. The temperature (T) dependence of K₁ indicates that the ¹³C hyperfine coupling (A^spin) has both an isotropic part (A_iso^spin) and an anisotropic part (A_ax^spin) with A_iso^spin/A_ax^spin = 0.78. Substantial decrease in the spin susceptibility (i.e. X^spin(T_c)/X^spin(300K) = 0.55) is not explained by the lattice contraction alone. The Knight shift values can be deduced experimentally without assuming the chemical shift values, since our analysis shows that the line shapes below T_c are affected negligibly by the magnetic-field distribution, which is consistent with the large penetration depth. We also showed the validity and consistency of our analysis.