Superconductivity at 18 K in potassium-doped C₆₀

THE synthesis of macroscopic amounts of C₆₀ and C₇₀ (fullerenes)¹ has stimulated a variety of studies on their chemical and physical properties^2,3. We recently demonstrated that C₆₀ and C₇₀ become conductive when doped with alkali metals⁴. Here we describe low-temperature studies of potassium-doped C₆₀ both as films and bulk samples, and demonstrate that this material becomes superconducting. Superconductivity is demonstrated by microwave, resistivity and Meissner-effect measurements. Both polycrystalline powders and thin-film samples were studied. A thin film showed a resistance transition with an onset temperature of 16 K and essentially zero resistance near 5 K. Bulk samples showed a well-defined Meissner effect and magnetic-field-dependent microwave absorption beginning at 18 K. The onset of superconductivity at 18 K is the highest yet observed for a molecular superconductor.