Browsing by Author "Harriger, Leland W."

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    Effect of Pnictogen Height on Spin Waves in Iron Pnictides
    (American Physical Society, 2014) Zhang, Chenglin; Harriger, Leland W.; Yin, Zhiping; Lv, Weicheng; Wang, Miaoyin; Tan, Guotai; Song, Yu; Abernathy, D.L.; Tian, Wei; Egami, Takeshi; Haule, Kristjan; Kotliar, Gabriel; Dai, Pengcheng
    We use inelastic neutron scattering to study spin waves in the antiferromagnetic ordered phase of iron pnictide NaFeAs throughout the Brillouin zone. Comparing with the well-studied AFe2As2 (A=Ca, Sr, Ba) family, spin waves in NaFeAs have considerably lower zone boundary energies and more isotropic effective in-plane magnetic exchange couplings. These results are consistent with calculations from a combined density functional theory and dynamical mean field theory and provide strong evidence that pnictogen height controls the strength of electron-electron correlations and consequently the effective bandwidth of magnetic excitations.
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    Possible Mott transition in layered Sr2Mn3As2O2ﾠsingle crystals
    (American Physical Society, 2019) Chen, Chih-Wei; Wang, Weiyi; Loganathan, Vaideesh; Carr, Scott V.; Harriger, Leland W.; Georgen, C.; Nevidomskyy, Andriy H.; Dai, Pengcheng; Huang, C.-L.; Morosan, E.
    Single crystals of Sr2Mn3As2O2 have been grown for the first time, for which we show a possible layer-selective Mott insulator behavior. This compound stands out as a hybrid structure of MnO2 and MnAs layers, analogously to the active CuO2 and FeAs layers, respectively, in the cuprate and iron-based high-temperature superconductors. Electrical transport, neutron diffraction measurements, together with density functional theory calculations on Sr2Mn3As2O2 single crystals converge toward a picture of independent magnetic order at T1∼79 K and T2∼360 K for the two Mn sublattices, with insulating behavior at odds with the metallic behavior predicted by calculations. Furthermore, our inelastic neutron-scattering studies of spin-wave dispersions for the Mn(1) sublattice reveal an effective magnetic exchange coupling of SJ∼3.7 meV. This is much smaller than those for the Mn(2) sublattice.
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    Short-range cluster spin glass near optimal superconductivity in BaFe2−xNixAs2
    (American Physical Society, 2014) Lu, Xingye; Tam, David W.; Zhang, Chenglin; Luo, Huiqian; Wang, Meng; Zhang, Rui; Harriger, Leland W.; Keller, T.; Keimer, B.; Regnault, L.-P.; Maier, Thomas A.; Dai, Pengcheng
    High-temperature superconductivity in iron pnictides occurs when electrons are doped into their antiferromagnetic (AF) parent compounds. In addition to inducing superconductivity, electron doping also changes the static commensurate AF order in the undoped parent compounds into short-range incommensurate AF order near optimal superconductivity. Here we use neutron scattering to demonstrate that the incommensurate AF order in BaFe2−xNixAs2 is not a spin-density wave arising from the itinerant electrons in nested Fermi surfaces, but is consistent with a cluster spin glass in the matrix of the superconducting phase. Therefore, optimal superconductivity in iron pnictides coexists and competes with a mesoscopically separated cluster spin glass phase, much different from the homogeneous coexisting AF and superconducting phases in the underdoped regime.
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    Spin Waves in Detwinned BaFe2As2
    (American Physical Society, 2018) Lu, Xingye; Scherer, Daniel D.; Tam, David W.; Zhang, Wenliang; Zhang, Rui; Luo, Huiqian; Harriger, Leland W.; Walker, H.C.; Adroja, D.T.; Andersen, Brian M.; Dai, Pengcheng
    Understanding magnetic interactions in the parent compounds of high-temperature superconductors forms the basis for determining their role for the mechanism of superconductivity. For parent compounds of iron pnictide superconductors such as AFe_{2}As_{2} (A=Ba, Ca, Sr), although spin excitations have been mapped out throughout the entire Brillouin zone, the respective measurements were carried out on twinned samples and did not allow for a conclusive determination of the spin dynamics. Here we use inelastic neutron scattering to completely map out spin excitations of ∼100% detwinned BaFe_{2}As_{2}. By comparing observed spectra with theoretical calculations, we conclude that the spin excitations can be well described by an itinerant model when taking into account moderate electronic correlation effects.