Electron-electron interactions and superconducting fluctuations in weakly localizedK3C60

Magnetotransport studies on superconducting ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ films are presented. These films are a three-dimensional (3D) weakly localized system with strong electron-electron interactions, reflected by the large positive magnetoresistance (MR). The effects of superconducting fluctuations on the MR are observed in this 3D weakly localized system. The localization is primarily caused by doping-induced disorder rather than granularity and the upper critical field ${\mathit{H}}_{\mathit{c}2}$(T) follows the Werthamer-Helfand-Hohenberg model. An electron mean free path of 10–20 Å is estimated in the normal state just above ${\mathit{T}}_{\mathit{c}}$.