X-Ray spectra and electronic correlations of FeSe1–xTex

Critical issues concerning emerging Fe-based superconductors include the degree of electron correlation and the origin of the superconductivity. X-Ray absorption spectra (XAS) and resonant inelastic X-ray scattering spectra (RIXS) of FeSe1−xTex (x = 0–1) single crystals were obtained to study their electronic properties that relate to electron correlation and superconductivity. The linewidth of Fe L2,3-edges XAS of FeSe1−xTex is narrower than that of Fe–pnictides, revealing the difference between their hybridization effects and localization character and those of other Fe–pnictides. While no significant differences exist between the Fe L-edge XAS and RIXS of FeSe1−xTex and those of Fe–pnictides, Se K-edge and Te K-edge XAS exhibit substantial edge shift, suggesting that the superconductivity in an Fe–Se superconductor is strongly associated with the ligand states. A comparison of the Se K-edge and Te K-edge spectra reveals that the charge transfer may occur between Se and Te. Given the Coulomb interaction and the bandwidth, the spectral results indicate that FeSe1−xTex is unlikely to be a weakly correlated system unlike the Fe–pnictides of the “1111” and “122” families. The spectral results further demonstrate that superconductivity in this class of Fe-based compounds is strongly associated with the ligand 4p hole state.