利用非弹性中子散射研究最佳掺杂 CaFe$_{0.88}$Co$_{0.12}$AsF 超导体中的低能自旋激发
Low-energy spin excitations in optimally doped CaFe$_{0.88}$Co$_{0.12}$AsF superconductor studied with inelastic neutron scattering
AI总结：
本文利用 INS 研究最佳电子掺杂 CaFe$0.88Co0.12AsF 单晶，发现12 meV 自旋共振模具有铁基超导体中最大的 Er/kBTc 比值，并支持自旋涨落介导的 s± 波配对。
摘要：
尽管 FeAs-1111 体系早在2008年即被发现，但由于大尺寸单晶生长极其困难，关于其超导单晶的非弹性中子散射（INS）研究报道很少。本文中，我们利用 INS 研究了 $T_\mathrm{c}$ = 21 K 的最佳电子掺杂 CaFe$_{0.88}$Co$_{0.12}$AsF 单晶中的低能自旋激发。超导自旋共振模的共振能量为 $E_\mathrm{r}$ = 12 meV，相当于 6.6 $k_\mathrm{B}T_\mathrm{c}$，构成了迄今报道的铁基超导体中最大的 $E_\mathrm{r}/k_\mathrm{B}T_\mathrm{c}$ 比值。这一大比值表明 CaFe$_{0.88}$Co$_{0.12}$AsF 中传导电子与磁激发之间存在强耦合。由于正常态 $ab$ 面内自旋-自旋关联长度的各向异性，该共振沿横向具有类磁振子的向上色散，这指向 CaFe$_{0.88}$Co$_{0.12}$AsF 中由自旋涨落介导的符号反转 ${s}\mathbf\pm$ 波配对。
英文摘要：
There are few inelastic neutron scattering (INS) reports on the superconducting single crystals of FeAs-1111 system, even though it was first discovered in 2008, due to the extreme difficulty in large single crystal growth. In this paper, we have studied the low-energy spin excitations in the optimally electron-doped CaFe$_{0.88}$Co$_{0.12}$AsF single crystals with $T_\mathrm{c}$ = 21 K by INS. The resonance energy of the superconducting spin resonant mode with $E_\mathrm{r}$ = 12 meV amounts to 6.6 $k_\mathrm{B}$$T_\mathrm{c}$, which constitutes the largest $E_\mathrm{r}$/$k_\mathrm{B}$$T_\mathrm{c}$ ratio among iron-based superconductors reported to date. The large ratio implies a strong coupling between conduction electrons and magnetic excitations in CaFe$_{0.88}$Co$_{0.12}$AsF. The resonance possesses a magnonlike upward dispersion along transverse direction due to the anisotropy of spin-spin correlation length within $ab$ plane in the normal-state, which points to a spin fluctuation mediated sign-reversed ${s}\mathbf\pm$ wave pairing in CaFe$_{0.88}$Co$_{0.12}$AsF.
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