Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr3
Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr3
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二维铁磁体 CrBr3 中的拓扑磁振子绝缘体自旋激发
DOI：
10.1103/physrevb.104.l020402
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发表时间：
2021-07-02
影响因子：
3.7
通讯作者：
Wen, Jinsheng
中科院分区：
文献类型：
--
作者：
Cai, Zhengwei;Bao, Song;Wen, Jinsheng
拓扑磁振子是电子系统中拓扑费米子的玻色子类似物。它们在理论上得到了广泛的研究，但很少通过实验实现。在这里，通过对二维铁磁体CrBr 3单晶进行非弹性中子散射测量，我们完全绘制出磁激发谱，并揭示在K点处磁振子的声学和光学分支之间存在类似于3.5 meV的明显间隙。CrBr 3被归类为狄拉克磁振子半金属，其特征在于狄拉克点处的线性带交叉。通过实验和理论计算之间的合作，使用从第一性原理计算获得的五轨道Hubbard模型来推导交换参数，我们发现，与海森堡交换相互作用，次近邻Dzyaloshinskiii-Moriya（DM）相互作用和单离子各向异性的哈密顿量更适合描述系统。使用该模型的计算表明，由差距分开的上下磁振子带表现出+/- 1的陈数。这些结果表明CrBr 3是一个拓扑磁振子绝缘体，其中非平凡的间隙是DM相互作用的结果。
Topological magnons are bosonic analogues of topological fermions in electronic systems. They have been studied extensively by theory but rarely realized by experiment. Here, by performing inelastic neutron scattering measurements on single crystals of a two-dimensional ferromagnet CrBr3, which was classified as Dirac magnon semimetal featured by the linear bands crossing at the Dirac points, we fully map out the magnetic excitation spectra, and reveal that there is an apparent gap of similar to 3.5 meV between the acoustic and optical branches of the magnons at the K point. By collaborative efforts between experiment and theoretical calculations using a five-orbital Hubbard model obtained from first-principles calculations to derive the exchange parameters, we find that a Hamiltonian with Heisenberg exchange interactions, next-nearest-neighbor Dzyaloshinskii-Moriya (DM) interaction, and single-ion anisotropy is more appropriate to describe the system. Calculations using the model show that the lower and upper magnon bands separated by the gap exhibit Chern numbers of +/- 1. These results indicate that CrBr3 is a topological magnon insulator, where the nontrivial gap is a result of the DM interaction.