Synthesis and superconducting properties of aRb3C60single crystal

Abstract

A pristine ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ single crystal with larger than millimeter dimensions was prepared by reaction of rubidium vapor with a seed-grown ${\mathrm{C}}_{60}$ single crystal (which exhibited remarkably sharp x-ray-diffraction peaks). A narrow superconducting transition width \ensuremath{\Delta}${\mathrm{T}}_{\mathrm{c}}$ (5--85% diamagnetic shielding) of the ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ single crystal is less than 1 K. The onset of the transition was at a temperature, ${\mathrm{T}}_{\mathrm{c}}$=30.0tK. Measurements of temperature dependence of the zero-field-cooled and field-cooled dc magnetization (using ten applied magnetic fields up to 5.0 T) are reported here. These and magnetization vs field data at different temperatures (ranging from 2 to 29 K) have been used to determine thermodynamic superconducting parameters, including the lower [${\mathrm{H}}_{\mathrm{c}1}$(T)] and upper [${\mathrm{H}}_{\mathrm{c}2}$(T)] critical fields, the Ginsburg-Landau coherence length \ensuremath{\xi}, and the London or Ginzburg-Landau penetration depth, \ensuremath{\lambda}. These are significantly different from those extracted from similar data in the literature for powder specimens. Hysteresis and magnetic relaxation measurements have been used to determine the nominal critical current density ${\mathrm{J}}_{\mathrm{c}}$(H,T) and the effective-pinning potential ${\mathrm{U}}_{\mathrm{eff}}$(J,H), respectively.