Ren Zheng, Huang Jianwei, Tan Hengxin, Biswas Ananya, Pulkkinen Aki, Zhang Yichen, Xie Yaofeng, Yue Ziqin, Chen Lei, Xie Fang, Allen Kevin, Wu Han, Ren Qirui, Rajapitamahuni Anil, Kundu Asish K, Vescovo Elio, Kono Junichiro, Morosan Emilia, Dai Pengcheng, Zhu Jian-Xin, Si Qimiao, Minár Ján, Yan Binghai, Yi Ming
Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA.
Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel.
Nat Commun. 2024 Oct 30;15(1):9376. doi: 10.1038/s41467-024-53722-3.
Magnetic kagome materials provide a fascinating playground for exploring the interplay of magnetism, correlation and topology. Many magnetic kagome systems have been reported including the binary FeX (X = Sn, Ge; m:n = 3:1, 3:2, 1:1) family and the rare earth RMnSn (R = rare earth) family, where their kagome flat bands are calculated to be near the Fermi level in the paramagnetic phase. While partially filling a kagome flat band is predicted to give rise to a Stoner-type ferromagnetism, experimental visualization of the magnetic splitting across the ordering temperature has not been reported for any of these systems due to the high ordering temperatures, hence leaving the nature of magnetism in kagome magnets an open question. Here, we probe the electronic structure with angle-resolved photoemission spectroscopy in a kagome magnet thin film FeSn synthesized using molecular beam epitaxy. We identify the exchange-split kagome flat bands, whose splitting persists above the magnetic ordering temperature, indicative of a local moment picture. Such local moments in the presence of the topological flat band are consistent with the compact molecular orbitals predicted in theory. We further observe a large spin-orbital selective band renormalization in the Fe spin majority channel reminiscent of the orbital selective correlation effects in the iron-based superconductors. Our discovery of the coexistence of local moments with topological flat bands in a kagome system echoes similar findings in magic-angle twisted bilayer graphene, and provides a basis for theoretical effort towards modeling correlation effects in magnetic flat band systems.
磁性 kagome 材料为探索磁性、关联和拓扑之间的相互作用提供了一个引人入胜的研究平台。已经报道了许多磁性 kagome 体系，包括二元 FeX（X = Sn、Ge；m:n = 3:1、3:2、1:1）族和稀土 RMnSn（R = 稀土）族，在顺磁相中，它们的 kagome 平带被计算为接近费米能级。虽然预计部分填充 kagome 平带会产生斯托纳型铁磁性，但由于这些体系的有序温度较高，尚未有关于这些体系在整个有序温度范围内磁分裂的实验可视化报道，因此 kagome 磁体中的磁性本质仍是一个悬而未决的问题。在这里，我们利用角分辨光电子能谱对通过分子束外延合成的 kagome 磁体薄膜 FeSn 的电子结构进行了探测。我们识别出了交换分裂的 kagome 平带，其分裂在高于磁有序温度时仍然存在，这表明存在局域磁矩图像。在拓扑平带存在的情况下，这种局域磁矩与理论预测的紧凑分子轨道一致。我们还在 Fe 自旋多数通道中观察到了大的自旋 - 轨道选择性能带重整化，这让人联想到铁基超导体中的轨道选择性关联效应。我们在 kagome 体系中发现局域磁矩与拓扑平带共存，这与魔角扭曲双层石墨烯中的类似发现相呼应，并为理论上模拟磁性平带体系中的关联效应提供了基础。
