Browsing by Author "Kamazawa, K"

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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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    Giant magnetic in-plane anisotropy and competing instabilities in Na3Co2SbO6
    (American Physical Society, 2022-12-02) Li, XT; Gu, YC; Chen, Y; Garlea, VO; Iida, K; Kamazawa, K; Li, YM; Deng, GC; Xiao, Q; Zheng, XQ; Ye, Z; Peng, YY; Zaliznyak, IA; Tranquada, JM; Li, Y
    We report magnetometry data obtained on twin-free single crystals of Na3Co2SbO6, which is considered a candidate material for realizing the Kitaev honeycomb model for quantum spin liquids. Contrary to a common belief that such materials can be modeled with the symmetries of an ideal honeycomb lattice, our data reveal a pronounced twofold symmetry and in-plane anisotropy of over 200%, despite the honeycomb layer’s tiny orthorhombic distortion of less than 0.2%. We further use magnetic neutron diffraction to elucidate a rich variety of field-induced phases observed in the magnetometry. These phases manifest themselves in the paramagnetic state as diffuse scattering signals associated with competing ferromagnetic and antiferromagnetic instabilities, consistent with a theory that also predicts a quantum spin liquid phase nearby. Our results call for theoretical understanding of the observed in-plane anisotropy and render Na3Co2SbO6 a promising ground for finding exotic quantum phases by targeted external tuning. © Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.