Production of single-crystal K3C60

A simplified technique for synthesizing high-quality millimeter-sized single-crystals of K₃C₆₀ is reported. The preparation method consists of a two-step process where pure C₆₀ crystals are first grown and later doped with potassium vapor. The undoped crystals are grown using an open-tube vapor transport with a flowing helium gas carrier. Doping occurs in a highvacuum environment inside a specialized quartz tube which allows phase purity to be monitored via magnetization measurements of the superconducting state. Utilizing the aforementioned procedure, one can attain samples with magnetically determined superconducting transition widths (10–90% diamagnetic shielding) of less than 1 K.