Initial considerations lead one to suspect that effects of strong correlation might be present in the alkali fulleride superconductors. We report direct measurements of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ $T_1$ anisotropy at 80 K in ${\mathrm{Rb}}_2$Cs${\mathrm{C}}_{60}$ and compare, in the context of the Korringa relation, the inferred spin-dipolar contribution to $\frac{1}{T_1}$ with the widths of the measured powder pattern line shape. The results demonstrate that the Korringa relation, valid in the limit of noninteracting electrons, holds in this case. Taken together with other normal-state NMR behavior this result makes important effects of strong correlation appear unlikely.

• Received 5 September 1995

DOI:https://doi.org/10.1103/PhysRevB.53.R2967