Evolution of Superconducting and Normal-State Properties in C60 “Polymer” Doped with K

Abstract:

Bulk superconductivity was observed in a new iodine-treated aggregated form of solid C₆₀, believed to be a “polymer”, by doping with alkali metal. Evolution of superconducting (T_c = 17.2 K) and normal-state properties, has been studied as a function of doping with K. The normal-state dc susceptibility exhibited a complex behavior with the increasing K uptake, evolving from an enhanced paramagnetism at low doping level, to a weakly temperature-dependent diamagnetism at the optimum doping level for superconductivity, and ending with a strong temperature-independent diamagnetism in over-doped samples. The measured superconductivity parameters, such as T_c, London penetration depth and the Ginzburg-Landau coherence length, are compared with those of the monomer K₃C₆₀. and the main factors determining the differences between the two systems are discussed.