Neutron Spin Resonance in a Quasi-Two-Dimensional Iron-Based Superconductor.

作者：Wenshan Hong, Linxing Song, Bo Liu, Ze Li, Zhenyuan Zeng, Yang Li, Dingsong Wu, Q. Sui, T. Xie, S. Danilkin, H. Ghosh, Abyay Ghosh, Jiangping Hu, Lin Zhao, Xingjiang Zhou, X. Qiu, Shiliang Li, Huiqian Luo · 发表于：Physical Review Letters · 年份：2020 · DOI：10.1103/PHYSREVLETT.125.117002 · 被引用次数：21 · 研究领域：Physics、Medicine

The neutron spin resonance is generally regarded as a key to understanding the magnetically mediated Cooper pairing in unconventional superconductors. Here, we report an inelastic neutron scattering study on the low-energy spin excitations in a quasi-two-dimensional iron-based superconductor KCa_{2}Fe_{4}As_{4}F_{2}. We have discovered a two-dimensional spin resonant mode with downward dispersions, a behavior closely resembling the low branch of the hourglass-type spin resonance in cuprates. While the resonant intensity is predominant by two broad incommensurate peaks near Q=(0.5,0.5) with a sharp energy peak at E_{R}=16  meV, the overall energy dispersion of the mode exceeds the measured maximum total gap Δ_{tot}=|Δ_{k}|+|Δ_{k+Q}|. These results deeply challenge the conventional understanding of the resonance modes as magnetic excitons regardless of underlining pairing symmetry schemes, and it also points out that when the iron-based superconductivity becomes very quasi-two-dimensional, the electronic behaviors are similar to those in cuprates.