Critical magnetic fields of superconducting Ba6C60

We have measured the upper and lower critical fields of superconducting Ba6C60. Near Tc, from the slope of the measured upper critical field, dHc2/dT=0.45 T/K, we obtain the zero-temperature Ginzburg-Landau coherence length as GL=120. Using the lower critical-field data, the penetration depth at T=0 is estimated to be (0)=1800. Combining (0) with the value of GL, we estimate the Fermi energy EF to be =0.15 eV. Thus, in comparison with the alkali-metal-doped fullerenes, the superconducting parameters Hc2, GL, and the resulting Ginzburg-Landau parameter , are significantly different in the case of the superconducting Ba-doped fullerene.