Anisotropic conductivity of Nd_{1.85}Ce_{0.15}CuO_{4-\delta} films at submillimeter wavelengths

The anisotropic conductivity of thin Nd${}_{1.85}$Ce${}_{0.15}$CuO${}_{4-\delta }$ films was measured in the frequency range 8 cm${}^{-1}<\nu <$ 40 cm${}^{-1}$ and for temperatures 4 K $<T<300$ K. A tilted sample geometry allowed 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_{{\rm C}%} the c-axis dielectric constant ${ϵ}_{1c}$ 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.