Magnetic-field penetration depth in K3C60 measured by muon spin relaxation

THE discovery1–3 of superconductivity in C60 doped with the alkali metals potassium and rubidium has introduced a new family of three-dimensional molecular superconductors4. The potassium-doped compound3 K3C60 has a relatively high transition temperature (Tc = 19.3K), a very high upper critical field (Hc2 (T⇒ 0)≈50T) and a short superconducting coherence length5 (£ = 26 Å), in common with the copper oxide superconductors. Here we report …