DOUBLE-RESONANCE NMR PROBES OF STRUCTURAL DISTORTIONS IN ALKALI-METAL-FULLERIDE SUPERCONDUCTORS

The Rb-87 NMR line shape of the Rb3C60 superconductor contains three d istinct peaks: one associated with octahedrally coordinated Rb in the fee lattice of C-60 molecules and two others, labeled T and T', both a ssociated with tetrahedrally coordinated Rb. This contrasts with the a ccepted crystal structure, in which all tetrahedral Rb sites are equiv alent. We report multinuclear single and double resonance NMR experime nts which probe for effects which could lead to the unexpected splitti ng, and discuss implications for electronic structure.