Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through C-13 NMR spin lattice relaxation (Tr) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A(4)C(60) This establishes that Jahn-Teller distortions (JTD) a nd strong electronic correlations must be considered to understand the beha vior of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T-1 is also detected for C-13 and Cs-133 NMR, implying the occurrence of excitations typical of JT disto rted C-60(2-) (or equivalently C-60(4-)). This supports the idea that dynam ic JTD can induce attractive electronic interactions in odd electron system s.