Orientational ordering and electron-phonon interaction in K₃C₆₀ superconductor

The normal state and superconducting state properties of a well characterized K₃C₆₀ superconductor are studied in terms of the combined measurements of x-ray diffraction, Raman scattering, magnetization, and resistivity by using the same sample synthesized by the wet chemical method. The temperature downshift of about 50 K is observed for the orientational ordering from pristine C₆₀ to the synthesized sample based on the anomalies of both the resistivity and phonon frequency. When entering the superconducting state, the enhanced self-energy effects are reflected from the softening and broadening of the phonon modes. The obtained electron-phonon interaction strength of 0.63 in the superconducting state accounts well for the transition temperature of 18 K in K₃C₆₀ and the plausible Coulomb pseudopotential and expected isotope exponent.