Browsing by Author "Li, Yuan"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Longitudinal Spin Excitations and Magnetic Anisotropy in Antiferromagnetically Ordered BaFe2As2
    (American Physical Society, 2013) Wang, Chong; Zhang, Rui; Wang, Fa; Luo, Huiqian; Regnault, L.P.; Dai, Pengcheng; Li, Yuan
    We report on a spin-polarized inelastic neutron-scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c axis, perpendicular to the ordering direction in the ab plane and parallel to the ordering direction. While the first two “transverse” components can be described by a linear spin-wave theory with magnetic anisotropy and interlayer coupling, the third “longitudinal” component is generically incompatible with the local-moment picture. It points toward a contribution of itinerant electrons to the magnetism that is already in the parent compound of this family of Fe-based superconductors.
  • Thumbnail Image
    Item
    Nematic Crossover in BaFe2As2 under Uniaxial Stress
    (American Physical Society, 2015) Ren, Xiao; Duan, Lian; Hu, Yuwen; Li, Jiarui; Zhang, Rui; Luo, Huiqian; Dai, Pengcheng; Li, Yuan
    Raman scattering can detect spontaneous point-group symmetry breaking without resorting to single-domain samples. Here, we use this technique to study BaFe2As2, the parent compound of the “122” Fe-based superconductors. We show that an applied compression along the Fe-Fe direction, which is commonly used to produce untwinned orthorhombic samples, changes the structural phase transition at temperature Ts into a crossover that spans a considerable temperature range above Ts. Even in crystals that are not subject to any applied force, a distribution of substantial residual stress remains, which may explain phenomena that are seemingly indicative of symmetry breaking above Ts. Our results are consistent with an onset of spontaneous nematicity only below Ts.
  • Thumbnail Image
    Item
    Nematic magnetoelastic effect contrasted between Ba(Fe1−xCox)2As2 and FeSe
    (American Physical Society, 2016) Hu, Yuwen; Ren, Xiao; Zhang, Rui; Luo, Huiqian; Kasahara, Shigeru; Watashige, Tatsuya; Shibauchi, Takasada; Dai, Pengcheng; Zhang, Yan; Matsuda, Yuji; Li, Yuan
    To elucidate the origin of nematic order in Fe-based superconductors, we report a Raman scattering study of lattice dynamics, which quantify the extent of C4-symmetry breaking, in BaFe2As2 and FeSe. FeSe possesses a nematic ordering temperature Ts and orbital-related band-energy split below Ts that are similar to those in BaFe2As2, but unlike BaFe2As2 it has no long-range magnetic order. We find that the Eg phonon-energy split in FeSe becomes substantial only well below Ts, and its saturated value is much smaller than that in BaFe2As2. Together with reported results for the Ba(Fe1−xCox)2As2 family, the data suggest that magnetism exerts a major influence on the lattice.