We investigate the far-infrared and submillimeter-wave conductivity of electron-doped ${\mathrm{La}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ tilted $1°$ off from the $\mathrm{ab}$-plane. The effective conductivity measured for this tilt angle reveals an intensive peak in the normal-state at finite frequency $\left(\nu \sim 50{\mathrm{cm}}^{-1}\right)$ due to a mixing of the in-plane and out-of-plane responses. The peak disappears for the pure in-plane response and transforms into a pure Drude-like contribution. A comparative analysis of the mixed and the in-plane spectra allows us to extract the c-axis conductivity which shows a Josephson plasma resonance at $\nu \simeq 11.7{\mathrm{cm}}^{-1}$ in the superconducting state.

• Received 1 July 2002

DOI:https://doi.org/10.1103/PhysRevB.66.212508