Normal-state optical properties of Nd1.85Ce0.15CuO4+δ

We present a detailed temperature dependence of the far-infrared reflectance for Nd1.85Ce0.15CuO4+δ films grown by pulsed-laser deposition. The reflectance spectra clearly show the presence of a ledge at 420 cm-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 Nd1.85Ce0.15CuO4+δ 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.