Far-infrared optical properties of the carbide superconductor ${\mathrm{Y}}_2{\mathrm{C}}_2{\mathrm{I}}_2$

The optical properties of the layered superconductor ${\mathrm{Y}}_2{\mathrm{C}}_2{\mathrm{I}}_2$ ${(T}_c=10\mathrm{}\hspace{0.5em}\mathrm{K})$ have been studied at far-infrared frequencies down to $5\hspace{0.5em}{\mathrm{cm}}^{-1}$ and at temperatures from 5 to 15 K, in superconducting and normal states. A clear manifestation of the superconducting transition has been observed in the reflectance spectra and in the Kramers-Kronig derived spectra of conductivity and dielectric permittivity. The normal-state spectra indicate an unusually low scattering rate of the charge carriers.