SUPERCONDUCTIVITY AT 30-K IN CESIUM-DOPED C60

RECENTLY there has been significant effort directed towards exploring the physical and chemical properties of C60 and other large carbon clusters 1-11. Particularly intriguing are reports of superconductivity in potassium- and rubidium-doped C60 Crystals and films 5-7. The transition temperatures (T(c)) for K-doped C60 (18 K) and Rb-doped C60 (approximately 28 K) are significantly higher than those reported previously for other molecular superconductors . Earlier attempts to prepare a caesium-doped superconducting phase 7 have proved unsuccessful. Here we report that a Cs-doped superconductor can be prepared by using as the dopant binary alloys of the type CsM (where M is Hg, Tl or Bi). We observe a reproducible superconducting transition in Cs(x)C60 (x = 1.2-3) at 30 K, demonstrated by flux expulsion (the Meissner effect) and flux exclusion (shielding) d.c. magnetization measurements. The low superconducting volume fraction (approximately 1%) suggests that further studies will be needed to determine the optimal doping concentration and to place tighter bounds on T(c).