Normal-state optical properties ofNd1.85Ce0.15CuO4+δ

We present a detailed temperature dependence of the far-infrared reflectance for ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$ films grown by pulsed-laser deposition. The reflectance spectra clearly show the presence of a ledge at 420 ${\mathrm{cm}}^{\mathrm{-}1}$ offering further evidence that this feature is common to all the cuprate superconductors. The optical conductivity obtained from Kramers-Kronig analysis can be divided into two components. The first component, which is strongly temperature dependent, is fit to a Drude model. This fit indicates that ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$ has a constant plasma frequency and a temperature-dependent scattering rate that closely follows the temperature dependence exhibited by the dc resistivity. The second component shows little temperature dependence and is described by a model that couples phonons to a midinfrared band. Comparisons between the optical conductivity and the structures seen by tunneling and inelastic-neutron-scattering measurements are made.