Infrared and optical properties of single-crystal YNi2B2C superconductor

We have determined the optical conductivity and other key spectral functions of single-crystal YNi2B2C for the spectral range of 5 meV - 4.1 eV via infrared reflectivity measurements and spectroscopic ellipsometry. Polished crystals and polished-and-annealed crystals were compared to understand the effect of annealing on the optical response. The conductivity spectrum of YNi2B2C exhibits metallic electronic response with the screened plasma frequency of 3.76 eV. The free-electron response is not well described by the Drude model alone. A number of interband transitions also appear beyond 1 eV. Their energies and JDOS critical-point types are analyzed on the basis of selection rules and results of band-structure calculations.