Inhomogeneous Electronic Structure of FeTe1-x Se x Revealed by X-ray Absorption Near Edge Structure

Ab initio Fe K-edge X-ray absorption near edge structure (XANES) calculations on FeTe1-x Se (x) , based on its crystallographic structure, are compared with experimental data. The calculated XANES spectra are inconsistent with the observed increase of spectral weight in the preedge region of the experimental spectra on the ternary system in which Te is substituted by Se. However, the weighted average of the XANES of FeTe and FeSe binaries reproduce well the observed trend in the experimental spectra of the ternary systems. This suggests that the FeTe1-x Se (x) is characterized by an inhomogeneous local electronic structure, resulting from a random-alloy like local atomic structure. The calculated unoccupied Fe d-density of states at the Fermi level increases monotonically with Te content unlike the observed change in T (c) with Te content. T (c) increases with increasing Te content up to x=0.5; however, the superconductivity is suppressed in the FeTe due to magnetic order, which is not considered in these calculations.