Metallic reflection spectra ofK3C60

Abstract

Optical reflectivity spectra were measured for the superconducting fulleride ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ and for pristine ${\mathrm{C}}_{60}$ single crystals in the wavelength region from infrared to ultraviolet. High-quality samples of ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ with flat surfaces were grown for this purpose by cosublimation of both ${\mathrm{C}}_{60}$ and potassium metal. A sharp plasma edge was found at 0.73 eV in the reflection spectra of ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$. A quantitative discussion is given on the conduction band structures based on the band parameters derived from a spectral shape analysis in terms of the Drude-Lorentz model.