Isotope effect in superconducting Rb3C60.

Measurements of the superconducting T c and Raman spectra in isotopically modified Rb 3 C 60 are reported. A decrease in T c of 0.65±0.10 K in samples with (75±5)% substitution of 13 C for 12 C yields an exponent of a=0.37±0.05. This is interpreted as evidence for phonon-mediated pairing