Song, YuMan, HaoranZhang, RuiLu, XingyeZhang, ChenglinWang, MengTan, GuotaiRegnault, L.-P.Su, YixiKang, JianFernandes, Rafael M.Dai, Pengcheng2017-02-242017-02-242016Song, Yu, Man, Haoran, Zhang, Rui, et al.. "Spin anisotropy due to spin-orbit coupling in optimally hole-doped Ba0:67K0:33Fe2As2." <i>Physical Review B,</i> 94, no. 21 (2016) American Physical Society: http://dx.doi.org/10.1103/PhysRevB.94.214516.https://hdl.handle.net/1911/94007We use polarized inelastic neutron scattering to study the temperature and energy dependence of spin space anisotropies in the optimally-hole-doped iron pnictide Ba0.67K0.33Fe2As2 (Tc=38 K). In the superconducting state, while the high-energy part of the magnetic spectrum is nearly isotropic, the low-energy part displays a pronounced anisotropy, manifested by a c-axis polarized resonance. We also observe that the spin anisotropy in superconducting Ba0.67K0.33Fe2As2 extends to higher energies compared with electron-doped BaFe2−xTMxAs2 (TM=Co, Ni) and isovalent-doped BaFe2As1.4P0.6, suggesting a connection between Tc and the energy scale of the spin anisotropy. In the normal state, the low-energy spin anisotropy for hole- and electron-doped iron pnictides near optimal superconductivity onset at temperatures similar to the temperatures at which the elastoresistance deviates from Curie–Weiss behavior, pointing to a possible connection between the two phenomena. Our results highlight the relevance of the spin-orbit coupling to the superconductivity of the iron pnictides.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlehttp://dx.doi.org/10.1103/PhysRevB.94.214516