SYNTHESIS AND SUPERCONDUCTING PROPERTIES OF A RB3C60 SINGLE-CRYSTAL

A pristine Rb3C60 single crystal with larger than millimeter dimension s was prepared by reaction of rubidium vapor with a seed-grown C-60 Si ngle crystal (which exhibited remarkably sharp x-ray-diffraction peaks ). A narrow superconducting transition width Delta T-c (5-85 % diamagn etic shielding) of the Rb3C60 Single crystal is less than 1 K. The ons et of the transition was at a temperature, T-c=30.0 K. Measurements of temperature dependence of the zero-field-cooled and field-cooled de m agnetization (using ten applied magnetic fields up to 5.0 T) are repor ted here. These and magnetization vs field data at different temperatu res (ranging from 2 to 29 K) have been used to determine thermodynamic superconducting parameters, including the lower [H-c1(T)] and upper [ H-c2(T)] critical fields, the Ginsburg-Landau coherence length xi, and the London or Ginzburg-Landau penetration depth, lambda. These are si gnificantly different from those extracted from similar data in the li terature for powder specimens. Hysteresis and magnetic relaxation meas urements have been used to determine the nominal critical current dens ity J(c)(H,T) and the effective-pinning potential U-eff(J,H), respecti vely.