Far-infrared properties and characterization of superconductingNb3Ge

The transmission and reflection of superconducting films of ${\mathrm{Nb}}_3$Ge have been measured from 20 to 90 ${\mathrm{cm}}^{\mathrm{-}1}$. Analysis using the Drude-Leplae formulation of the ac conductivity yields gap energies of 43 to 54 ${\mathrm{cm}}^{\mathrm{-}1}$ and normal-state electronic scattering times of (0.9–2.1)×${10}^{\mathrm{-}14}$ sec, in agreement with independent measurements. These results extend the validity of the Leplae approach for high-$T_c$ strong-coupled materials. The fits to the data also required an assumption of film inhomogene- ity, exploiting the large penetration depth of far-infrared radiation for materials characterization.