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 $\epsilon_{1c}$ 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. 
A. Pimenov, A. V. Pronin, A. Loidl, U. Michelucci, A. P. Kampf, S. I.   Krasnosvobodtsev, V. S. Nozdrin, and D. Rainer