Anisotropic conductivity ofNd1.85Ce0.15CuO4−δfilms at submillimeter wavelengths

The anisotropic conductivity of thin ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4-\delta }$ films was measured in the frequency range $8<\mathrm{}\nu <40\mathrm{}\hspace{0.5em}{\mathrm{cm}}^{-1}$ and for temperatures $4<T<\mathrm{}300\mathrm{}\hspace{0.5em}\mathrm{K}.$ A tilted sample geometry made it possible to extract both in-plane and c-axis properties. The in-plane quasiparticle scattering rate remains unchanged as the sample becomes superconducting. The temperature dependence of the in-plane conductivity is reasonably well described using the Born limit for a d-wave superconductor. Below $T_C,$ the c-axis dielectric constant ${\varepsilon }_{1c}$ changes sign at the screened c-axis plasma frequency. The temperature dependence of the c-axis conductivity closely follows the linear in T behavior within the plane.