Superconductivity appearing from C₆₀ doped with rare-earth metals

Abstract

The superconductivity observed in rare-earth C₆₀ fullerides RE_xC₆₀ (RE ¼ Yb and Sm) and La–C₆₀ compounds are described. It is shown that RE_2.75C₆₀’s do not superconduct and the true superconducting phase in Y–bC₆₀ fulleride resides in the t_1g band. No superconductivity is observed in Sm–C₆₀ fullerides. The phase sequence between Yb–C₆₀ fullerides and Sm–C₆₀ ones as a function of the intercalant concentration is shown to be greatly different, although Yb and Sm are the same family of divalent rare-earth elements. This seems to explain theloss of superconductivity in Sm_xC₆₀, and suggests that the true superconducting phase is most likely Yb_xC₆₀ ðx43Þ with the primitive cubic lattice. In addition, the superconductivity observed in C₆₀ with La is shown to result from La₂C₃ carbides with two transition temperatures.

Key words:

• Superconductivity
• Fullerenes and related materials