Dynamical conductivity of an MBE-grown La_1.84Sr_0.16CuO₄ thin film at frequencies from 5 to 36 cm^-1

We present the first wide-band (5-400 cm-1) measurements of the dynamical conductivity and the dielectric permittivity spectra of La2-xSrxCuO4 (x ≈ 0.16). A narrow Drude-like band is observed in the spectra, which is consistent with a d-wave pairing state. We determine the plasma frequency, scattering rate, and mean free path of the unpaired charge carriers responsible for this band. For the first time, "coherence peak"-like behavior is observed in the temperature dependence of the submillimeter conductivity of La2-xSrxCuO4, associated with the temperature evolution of the band in the superconducting state. Published by Elsevier Science B.V.