Superconducting phase sequence in RxC60 fullerides (R=Sm and Yb)

The true superconducting phase in rare-earth C-60 fullerides RxC60 (R=Yb and Sm) is not R2.75C60 previously reported. Moreover, no superconductivity is observed in Sm-C-60 fullerides. The phase sequence between Yb-C-60 fullerides and Sm-C-60 ones as a function of the intercalant concentration of x is shown to be greatly different, although Yb and Sm are the same family of rare-earth elements with the divalent valence state. This can explain the loss of superconductivity in SmxC60 and suggests the true superconducting phase. The whole picture of rare-earth C-60 fullerides is described.