Chen Lebing, Teng Xiaokun, Tan Hengxin, Winn Barry L, Granroth Garrett E, Ye Feng, Yu D H, Mole R A, Gao Bin, Yan Binghai, Yi Ming, Dai Pengcheng
Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA.
Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 7610001, Israel.
Nat Commun. 2024 Mar 1;15(1):1918. doi: 10.1038/s41467-023-44190-2.
The combination of a geometrically frustrated lattice, and similar energy scales between degrees of freedom endows two-dimensional Kagome metals with a rich array of quantum phases and renders them ideal for studying strong electron correlations and band topology. The Kagome metal, FeGe is a noted example of this, exhibiting A-type collinear antiferromagnetic (AFM) order at T ≈ 400 K, then establishes a charge density wave (CDW) phase coupled with AFM ordered moment below T ≈ 110 K, and finally forms a c-axis double cone AFM structure around T ≈ 60 K. Here we use neutron scattering to demonstrate the presence of gapless incommensurate spin excitations associated with the double cone AFM structure of FeGe at temperatures well above T and T that merge into gapped commensurate spin waves from the A-type AFM order. Commensurate spin waves follow the Bose factor and fit the Heisenberg Hamiltonian, while the incommensurate spin excitations, emerging below T where AFM order is commensurate, start to deviate from the Bose factor around T, and peaks at T. This is consistent with a critical scattering of a second order magnetic phase transition with decreasing temperature. By comparing these results with density functional theory calculations, we conclude that the incommensurate magnetic structure arises from the nested Fermi surfaces of itinerant electrons and the formation of a spin density wave order.
几何阻挫晶格与自由度之间相似的能量尺度相结合，赋予二维 Kagome 金属一系列丰富的量子相，并使其成为研究强电子关联和能带拓扑的理想材料。Kagome 金属 FeGe 就是一个显著的例子，它在 T ≈ 400 K 时呈现 A 型共线反铁磁（AFM）序，然后在 T ≈ 110 K 以下建立与 AFM 有序磁矩耦合的电荷密度波（CDW）相，最后在 T ≈ 60 K 附近形成 c 轴双锥 AFM 结构。在此，我们利用中子散射证明，在远高于 T 和 T 的温度下，FeGe 的双锥 AFM 结构存在无隙非 commensurate 自旋激发，这些激发会合并成来自 A 型 AFM 序的有隙 commensurate 自旋波。Commensurate 自旋波遵循玻色因子并符合海森堡哈密顿量，而在 AFM 序为 commensurate 的 T 以下出现的非 commensurate 自旋激发，在 T 附近开始偏离玻色因子，并在 T 处达到峰值。这与随着温度降低的二阶磁相变的临界散射相一致。通过将这些结果与密度泛函理论计算进行比较，我们得出结论，非 commensurate 磁结构源于巡游电子的嵌套费米面以及自旋密度波序的形成。
