Critical magnetic fields in the superconducting state ofK3C60

We have measured the temperature dependence of the lower and upper critical fields in superconducting ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$. From the measurements, we have evaluated the penetration depth (λ=2400 Å) and superconducting coherence length (ξ=26 Å). The parameters are in agreement with a superconducting state formed by a narrow band.