Anisotropic optical conductivity of Nd2-xCexCuO4 thin films

Optical conductivity spectra sigma (1)(omega) of Nd2-xCexCuO4 thin films, measured by the reflectance-transmittance method (R-T method) which has been proposed to investigate far-infrared spectroscopy, are investigated based on the anisotropic pairing model. Precise measurements of the frequency-dependent conductivity sigma (1)(omega) enable us to examine quantitatively the nature of the superconducting gap through infrared properties for the first time in high-T-c superconductors. We show that the behavior of optical conductivity sigma (1)(omega) is consistent with the anisotropic superconducting gap and is well explained by the formula for d-wave pairing in the far-infrared region. Our results suggest that the electron-doped cuprate superconductors Nd2-xCexCuO4 have nodes in the superconducting gap.