133Cs and 13C-NMR in CsC60 polymers under pressure

Alkali metal doped fullerides reveal a polymerized crystal structure with parallel chains of covalently bounded C60 molecules. The electronic structure shows a narrow π-electron band. The existence of strong electron-electron correlations in this fulleride is supported by the establishment of an antiferromagnetic ground state at TN=30K. We report the measurements of 133Cs and 13C-NMR relaxation rates on CsC60 polymers which have been performed versus pressure and temperature. Our results show that the hydrostatic pressure suppresses the antiferromagnetic order and stabilizes a spin-singlet long range order at 5kbar. A study of the quadrupolar spin-echo of 133Cs performed at ambient pressure reveals a second order structural transition at TS=13.8K towards a spin-singlet ground state which coexists with the preexisting antiferromagnetic order.