We use neutron polarization analysis to study spin excitation anisotropy in the optimally isovalent-doped superconductor ${\mathrm{BaFe}}_2$(${\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}$)${}_2$ ($T_c=30$ K). Different from optimally hole- and electron-doped ${\mathrm{BaFe}}_2{\mathrm{As}}_2$, where there is a clear spin excitation anisotropy in the paramagnetic tetragonal state well above $T_c$, we find no spin excitation anisotropy for energies above 2 meV in the normal state of ${\mathrm{BaFe}}_2$(${\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}$)${}_2$. Upon entering the superconducting state, significant spin excitation anisotropy develops at the antiferromagnetic (AF) zone center ${\mathbf{Q}}_{\mathrm{AF}}=(1,0,L=\mathrm{odd})$, while the magnetic spectrum is isotropic at the zone boundary $\mathbf{Q}=(1,0,L=\mathrm{even})$. By comparing the temperature, wave vector, and polarization dependence of the spin excitation anisotropy in ${\mathrm{BaFe}}_2$(${\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}$)${}_2$ and hole-doped ${\mathrm{Ba}}_{0.67}{\mathrm{K}}_{0.33}{\mathrm{Fe}}_2{\mathrm{As}}_2$ ($T_c=38$ K), we conclude that such anisotropy arises from spin-orbit coupling and is associated with the nearby AF order and superconductivity.

中文翻译：

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最佳等价掺杂超导体BaFe2（As0.7P0.3）2中的自旋激发各向异性

我们使用中子极化分析研究最佳等价掺杂超导体中的自旋激发各向异性 ${\mathrm{钡铁}}_{\mathrm{2个}}$（${\mathrm{作为}}_{0.7}{\mathrm{P}}_{0.3}$）${}_{\mathrm{2个}}$ （${Ť}_C=30$K）。与最佳的空穴和电子掺杂不同${\mathrm{钡铁}}_{\mathrm{2个}}{\mathrm{作为}}_{\mathrm{2个}}$，在正上方的顺磁性四边形状态下有明显的自旋激发各向异性 ${Ť}_C$，在正常状态下，对于2 meV以上的能量，我们没有发现自旋激发各向异性 ${\mathrm{钡铁}}_{\mathrm{2个}}$（${\mathrm{作为}}_{0.7}{\mathrm{P}}_{0.3}$）${}_{\mathrm{2个}}$。进入超导状态后，反铁磁（AF）区中心会产生明显的自旋激发各向异性${\mathbf{问}}_{\mathrm{自动对焦}}=（\mathrm{1个}，0，\mathrm{大号}=\mathrm{奇怪的}）$，而磁场谱在区域边界是各向同性的 $\mathbf{问}=（\mathrm{1个}，0，\mathrm{大号}=\mathrm{甚至}）$。通过比较温度，波矢和自旋激发各向异性的极化相关性${\mathrm{钡铁}}_{\mathrm{2个}}$（${\mathrm{作为}}_{0.7}{\mathrm{P}}_{0.3}$）${}_{\mathrm{2个}}$ 和空穴掺杂 ${巴}_{0.67}{\mathrm{ķ}}_{0.33}{铁}_{\mathrm{2个}}{\mathrm{作为}}_{\mathrm{2个}}$ （${Ť}_C=38$ K），我们得出这样的各向异性是由于自旋轨道耦合引起的，并且与附近的AF阶和超导性有关。