Electronic transport properties ofK3C60films

We report the longitudinal resistivity and Hall-effect data of thin films of ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ in the normal and superconducting states in magnetic fields up to 12.5 T. The resistivity is 2.5 mΩ cm at room temperature and near the metal-to-insulator transition. The Hall coefficient is small as expected for a half-filled conduction band, and changes sign at 220 K. The resistivity is interpreted in terms of the granularity of the film which leads to zero-dimensional superconductivity in these systems with a length scale of 70 Å. We find a superconducting coherence length of ∼26 Å, which we interpret as a single-grain property. The Pippard coherence length, i.e., in the absence of granularity, is estimated to be ∼150 Å.