Cluster Model Description of Polarized Cu K-Edge Spectra of Nd_(2-x)Ce_xCuO_(4-δ)

Single crystals Nd_(2-x)Ce_xCuO_(4-δ) with x=0.0 and 0.2 are studied by polarized X-ray absorption measurements at Cu K-edge. The positions and intensities of the 1s→ 4pσ transition features in the K-edge spectra are analyzed with a modified cluster model and functional curve fitting procedure. All of the experimental results including the energies of the spectral features, the energy separations between features and the variation of feature intensities, can be well explained by the cluster model parameters obtained from the curve fitting. Particularly, it is found that the charge transfer energy gap Δ in the Nd_(2-x)Ce_xCuO_(4-δ) system decreases from about 1.4 eV at x=0 to 0.5 eV at x = 0.2. Our analysis in this paper provides a method for quantitative X-ray absorption spectroscopy (XAS) study of the charge transfer gap for electron-doped cuprate superconductors and related materials.