1. Condensed-Matter Physics & Materials Science Seminar

    "Cu-induced localization in the Fe-based superconductor FeTe0.5Se0.5"

    Presented by Jinsheng Wen, National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing, China

    Thursday, March 28, 2013, 1:30 pm
    Small Seminar Room, Bldg. 510

    Hosted by: Genda Gu

    In the talk, I will describe our recent neutron scattering and resistivity results on the Cu-substitution effects in FeTe0.5Se0.5. With a 2% Cu substitution, Tc is reduced from 15 to 8 K. For Fe0.9Cu0.1Te0.5Se0.5, it is not superconducting. In this sample, the low-energy magnetic excitation around the in-plane wave vector (0.5, 0.5) is greatly enhanced. Upon heating, the magnetic scattering is weakened, which is different from the temperature dependences of the Cu-free and 2% Cu-doped sample. The spectral weight reduction upon warming decreases with increasing energy in the 10% Cu-doped sample. We take these as evidences that Cu drives the system towards localization, which is confirmed by our resistivity data. These observations probably explain why superconductivity is absent in the Cu-doped BaFe2As2 system and demonstrate the inadequacy of the rigid-band shift model on the substitution effects of the 3d transition metals.