Dielectric functions of La-based cuprate superconductors for visible and near-infrared wavelengths

The highly c-axis oriented La _1.9 Ce _0.1 CuO ₄ (LCCO) film was prepared on SrTiO ₃ (STO) substrate by pulsed-laser deposition (PLD). The identification and characterization of the LCCO film was determined by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Spectroscopic ellipsometry (SE) measurement was performed on the LCCO film in 0.5–4.13 eV range. The complex pseudodielectric function of the LCCO film was reported by Drude and Lorentz oscillators in this work. Critical point analysis on third-derivative spectra of the Lorentz contributions was accomplished to obtain the interband transition energies. The results indicate that the interband transitions are mainly related to the copper-oxygen planes. The metallic behavior of the pseudodielectric function, which is a common feature in all known electron-doped superconductors, can be obviously observed in the LCCO film.