Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Phys Rev Lett. 2018 Mar 30;120(13):137001. doi: 10.1103/PhysRevLett.120.137001.
We use inelastic neutron scattering to study the low-energy spin excitations of the 112-type iron pnictide Ca_{0.82}La_{0.18}Fe_{0.96}Ni_{0.04}As_{2} with bulk superconductivity below T_{c}=22 K. A two-dimensional spin resonance mode is found around E=11 meV, where the resonance energy is almost temperature independent and linearly scales with T_{c} along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any L modulations. Because of the unique monoclinic structure with additional zigzag arsenic chains, the As 4p orbitals contribute to a three-dimensional hole pocket around the Γ point and an extra electron pocket at the X point. Our results suggest that the energy and momentum distribution of the spin resonance does not directly respond to the k_{z} dependence of the fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.
我们利用非弹性中子散射研究了具有体超导性的 112 型铁磷化物 Ca_{0.82}La_{0.18}Fe_{0.96}Ni_{0.04}As_{2}的低能自旋激发。在 E=11 meV 左右发现了一个二维自旋共振模式，其中共振能量几乎与温度无关，并与其他铁基超导体一样随 T_{c}线性变化。极化中子分析表明，共振在自旋空间中几乎是各向同性的，没有任何 L 调制。由于具有额外的锯齿状砷链的独特单斜结构，As 4p 轨道在 Γ 点周围贡献了一个三维空穴口袋和 X 点处的一个额外电子口袋。我们的结果表明，自旋共振的能量和动量分布并不直接响应于费米子的 k_{z}依赖性，并且在弱自旋轨道耦合的情况下，自旋共振本质上是来自库珀对的单重态-三重态激发的自旋-1 模式。
