Browsing by Author "Xie, T"

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    Electron doping effects on the spin spectroscopy of BaFe2-xNixAs2 superconductors
    (International Conference on Neutron Scattering, 2017-07-12) Luo, HQ; Gong, DL; Xie, T; Lu, XY; Kamazawa, K; Iida, K; Kajimoto, R; Ivanov, AS; Adroja, DT; Kulda, J; Danilkin, SA; Deng, GC; Li, SL; Dai, PC
    High-temperature superconductivity in iron pnictides emerges from electron or hole doped parent compounds with antiferromagnetic order, which is argued to be associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons. With more than 6 years\' efforts, we have used time-of-flight neutron spectroscopy to extensively map out the spin excitations in the electron-doped BaFe2-xNixAs2 especially around the overdoped zone boundary of superconductivity. We have found that the high energy spin fluctuations survive in the extremely high doping x=0.6 far beyond the superconducting dome, but the low energy spin excitations including the spin resonance mode is very sensitive to the electron dopings, by finally forming a large spin gap just after the disappearance of superconductivity in the overdoped regime. Further polarized neutron analysis indicate that the spin gap actually is anisotropic, and the longitudinal mode of spin fluctuations, as a hallmark of the itinerant magnetism from Fermi surface nesting, is totally eliminated together with the hole pockets near the electron-overdoped zone boundary of superconductivity.Our results suggest that the strong fluctuations from local moments give framework for magnetic interaction, while itinerant spin excitations originated from Fermi surface nesting are crucial to the superconductivity in iron pnictides.
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    Preferred spin excitations in the bilayer iron-based superconductor CaKðFe0.96Ni0.04Þ4As4 with spin-vortex crystal order
    (American Physical Society, 2022-03-31) Liu, C; Bourges, P; Sidis, Y; He, GH; Bourdarot, F; Danilkin, SA; Ghosh, H; Ghosh, S; Ma, XY; Li, SL; Li, Y; Luo, HQ; Xie, T
    Spin-orbit coupling (SOC) is a key to understand the magnetically driven superconductivity in iron-based superconductors, where both local and itinerant electrons are present and the orbital angular momentum is not completely quenched. Here, we report a neutron scattering study on the bilayer compound CaK(Fe0.96Ni0.04)4As4 with superconductivity coexisting with a noncollinear spin-vortex crystal magnetic order that preserves the tetragonal symmetry of the Fe-Fe plane. In the superconducting state, two spin resonance modes with odd and even L symmetries due to the bilayer coupling are found similar to the undoped compound CaKFe4As4 but at lower energies. Polarization analysis reveals that the odd mode is c-axis polarized, and the low-energy spin anisotropy can persist to the paramagnetic phase at high temperature, which closely resembles other systems with in-plane collinear and c-axis biaxial magnetic orders. These results provide the missing piece of the puzzle on the SOC effect in iron-pnictide superconductors, and also establish a common picture of c-axis preferred magnetic excitations below Tc regardless of the details of magnetic pattern or lattice symmetry. © 2022 American Physical Society