Anomalous heat capacity and x-ray photoelectron spectroscopy of superconducting FeSe1/2Te1/2

The bulk polycrystalline sample FeSe1/2Te1/2 is synthesized via the solid state reaction route in an evacuated, sealed quartz tube at 750 degrees C. The presence of superconductivity is confirmed through magnetization/thermoelectric/resistivity studies. It is found that the superconducting transition temperature (T-c) is around 12 K. The heat capacity (C-p) of superconducting FeSe1-xTex exhibits a hump near T-c, instead of a well-defined lambda transition. X-ray photoelectron spectroscopy studies reveal well-defined positions for divalent Fe, Se, and Te, but with sufficient hybridization of the Fe (2p) and Se/Te (3d) core levels. In particular, divalent Fe is shifted to a higher binding energy, and Se and Te to a lower one. The situation is similar to that observed previously for the famous Cu-based high T-c superconductors, where the Cu (3d) orbital hybridizes with O (2p). We also found the satellite peak of Fe at 712.00 eV, which is attributed to the charge-carrier localization induced by Fe at the 2c site. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3556682]