Penetration depth and Ginzburg number in Rb 3C 60

Abstract

The penetration depth λ, the Ginzburg-Landau parameter κ and the Ginzburg number Gi in the superconducting fulleride Rb 3C 60 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 Rb 3C 60 turns out to be narrow enough, Gi ≈10 -4, indicating that superconducting fluctuations in fullerides are weaker than in high- T c oxide superconductors.