Optical properties of RNi₂B₂C (R = Y, Lu, Ho, Er) intermetallic borocarbide superconductors

We have studied the optical properties of single crystals of RNi₂B₂C (R = Y, Lu, Er, Ho) intermetallic superconductors over a wide range of energies from 50 cm^-1 to 100000 cm^-1 (6 meV to 12.4 eV) at room temperature by performing normal-incidence reflectivity measurements. The optical spectral functions of the four compounds show similar properties irrespective of the type of rare-earth ion or its magnetic moment. The optical conductivity of YNi₂B₂C at room temperature is reasonably well described by the simple Drude model for the electronic contribution and by six Lorentzian peaks representing interband transitions.