Carbon isotope effect in single-crystal Rb 3C 60

Abstract

We have synthesized single crystals of isotopically enriched Rb 3C 60. The very sharp superconducting transitions in single crystal superconducting fullerides allow us to determine the isotope effect on the superconducting transition temperature, T c, with unprecedented accuracy. We find that the carbon isotope shift exponent α carbon for 99% 13C. This coupled with near-zero significantly smaller than other values reported in the literature 1–6. This, coupled with the near-zero rubidium isotope effect reported by B. Burk et. al. 7, should place considerable constraints on any theoretical model of superconductivity in the alkali fullerides.