论文标题
基于双层铁的超导体Cakfe $ _4 $ as $ _4 $
Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe$_4$As$_4$
论文作者
论文摘要
我们使用偏光非弹性中子散射来研究基于双层铁的超导体cakfe $ _4 $ as $ _4 $（$ t_c $ = 35 k）中的自旋兴奋剂各向异性。在超导状态下，在我们以前的未极化中子散射实验中已经观察到了奇数甚至$ l- $调节的旋转共振（T. xie {\ it等人}Phys。Rev.lett。{\ bf 120}，267003（2018））。在这里，我们发现高能模式（$ \ sim 18 $ MEV）在旋转空间中是各向同性的，但是低能的奇数模式由$ c- $轴极化模式组成9 MEV附近9 MEV，以及另一种部分重叠的内置内部内置模式。我们认为，这种自旋各向异性是由这种独特化合物的自旋涡流波动中的自旋轨道耦合引起的。自旋各向异性受到超导性的强烈影响，在正常状态下，它在6 MEV下弱弱，然后转移到更高的能量，并在$ T_C $以下的旋转共振模式下进一步增强。
We use polarized inelastic neutron scattering to study the spin-excitations anisotropy in the bilayer iron-based superconductor CaKFe$_4$As$_4$ ($T_c$ = 35 K). In the superconducting state, both odd and even $L-$modulations of spin resonance have been observed in our previous unpolarized neutron scattering experiments (T. Xie {\it et al.} Phys. Rev. Lett. {\bf 120}, 267003 (2018)). Here we find that the high-energy even mode ($\sim 18$ meV) is isotropic in spin space, but the low-energy odd modes consist of a $c-$axis polarized mode around 9 meV along with another partially overlapped in-plane mode around 12 meV. We argue that such spin anisotropy is induced by the spin-orbit coupling in the spin-vortex-type fluctuations of this unique compound. The spin anisotropy is strongly affected by the superconductivity, where it is weak below 6 meV in the normal state and then transferred to higher energy and further enhanced in the odd mode of spin resonance below $T_c$.
