Penetration depth and Ginzburg number in Rb₃C₆₀

The penetration depth λ, the Ginzburg-Landau parameter κ and the Ginzburg number Gi in the superconducting fulleride Rb₃C₆₀ are estimated. To determine these quantities the results of recent magnetization measurements performed by Politis et al. on the fine powder specimen are analyzed. A finiteness of superconducting grain sizes is taken into account and shown to influence considerably the calculated values of λ and κ. The experimental data are found to be consistent with the assumption that λ(T) obeys the Ginzburg-Landau theory within the whole temperature range studied and result in λ(0)=2100 Å, κ ≈90. The estimated critical region in Rb₃C₆₀ turns out to be narrow enough, Gi ≈10^-4, indicating that superconducting fluctuations in fullerides are weaker than in high-T_c oxide superconductors.