Browsing by Author "Zhang, P."

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    Observation of Momentum-Confined In-Gap Impurity State in Ba0.6K0.4Fe2As2: Evidence for Antiphase s± Pairing
    (American Physical Society, 2014) Zhang, P.; Richard, P.; Qian, T.; Shi, X.; Ma, J.; Zeng, L.-K.; Wang, X.-P.; Rienks, E.; Zhang, C.-L.; Dai, Pengcheng; You, Y.-Z.; Weng, Z.-Y.; Wu, X.-X.; Hu, J.P.; Ding, H.
    We report the observation by angle-resolved photoemission spectroscopy of an impurity state located inside the superconducting gap of Ba 0.6 K 0.4 Fe 2 As 2 and vanishing above the superconducting critical temperature, for which the spectral weight is confined in momentum space near the Fermi wave-vector positions. We demonstrate, supported by theoretical simulations, that this in-gap state originates from weak scattering between bands with opposite sign of the superconducting-gap phase. This weak scattering, likely due to off-plane nonmagnetic (Ba, K) disorder, occurs mostly among neighboring Fermi surfaces, suggesting that the superconducting-gap phase changes sign within holelike (and electronlike) bands. Our results impose severe restrictions on the models promoted to explain high-temperature superconductivity in these materials.
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    Yield strength dependence on strain rate of molybdenum-alloy nanofibers
    (AIP Publishing LLC., 2014) Loya, P.E.; Xia, Y.Z.; Peng, C.; Bei, H.; Zhang, P.; Zhang, J.; George, E.P.; Gao, Y.F.; Lou, J.
    The yield strength dependence on strain rate was studied for molybdenum-alloy nanofibers with varying initialﾠdislocationﾠdensity at three different pre-strain levels.ﾠIn-situﾠtensile experiments at three displacement rates were carried out in aﾠscanning electron microscope.ﾠYield strength and its scatter decreased as a function of the pre-strain level for different displacement rates. Aﾠstatistical modelﾠwas used to analyze the results, and a negative strain rate dependence was inferred from the yield experiments. This finding suggests the need for theoretical investigations since classical models such as dynamic strain aging may have limitations at such nanoscales.