MIDINFRARED REFLECTIVITY OF SINGLE-CRYSTAL ND2-XCEXCU4O4-Y

We have measured infrared reflectivity of single crystals of Nd2-xCexCu4O4-y in the range between 0.05 eV and 1.5 eV. The superconducting or nearly superconducting crystals studied show a very high mid-IR reflectivity. Reflectivity of the samples is fitted much better with a Drude model, which yielded very similar fitting parameters (ωp ∼ 2.5 eV) for all samples, than YBa2Cu3O7 or Bi2Sr2CuO6. However, a deviation from a Drude model was evident in the very low frequency and the fitting was considerably improved with a Drude-Lorentz model in both fittings of the reflectivity and the frequency dependent conductivity. Further, no temperature dependence of the reflectivity above 0.2 eV was observed between 25K and 200K. The present study suggests the inapplicability of the Drude model to this system and supports the existence of the mid-IR absorption. © 1990.