Jin Lei, Wang Lirong, Zhang Xiaoming, Liu Ying, Dai Xuefang, Gao Hongli, Liu Guodong
State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300130, China.
Nanoscale. 2021 Mar 21;13(11):5901-5909. doi: 10.1039/d0nr07556f. Epub 2021 Mar 16.
The quantum anomalous Hall effect (QAHE) in intrinsic ferromagnets has attracted considerable attention recently. Previously, studies of the QAHE have mostly focused on the default assumption of out-of-plane magnetization. In fact, the QAHE can also be achieved via in-plane magnetization, but such candidate materials are very scarce. Here, we find that two-dimensional (2D) YN not only possesses the previously reported out-of-plane QAHE, but it also possesses a tunable in-plane QAHE. More importantly, unlike the previously reported in-plane QAHE in d/f-type ferromagnets, here we report the effect in a 2D d ferromagnet, namely YN, for the first time. In the ground state, a YN monolayer has a half-metal band structure, and manifests six pairs of fully spin-polarized Weyl points at the Fermi level. When spin-orbit coupling is included, the YN monolayer can realize multiple topological phases, determined based on the magnetization direction. Under in-plane magnetization, the YN monolayer shows either the Weyl state or in-plane QAHE state. Remarkably, the Chern number (±1) and the propagating direction of QAHE edge channels can be continuously switched via shifting the direction of the in-plane magnetic field. When magnetization is applied out-of-plane, the YN monolayer realizes an out-of-plane QAHE phase with a high Chern number of 3. The nontrivial edge states for all the topological phases in the YN monolayer have been clearly identified. This work suggests that 2D YN is an excellent candidate for investigating in-plane QAHE phases in d ferromagnets.
本征铁磁体中的量子反常霍尔效应（QAHE）近来备受关注。此前，对QAHE的研究大多集中在面外磁化的默认假设上。实际上，QAHE也可通过面内磁化来实现，但这类候选材料非常稀少。在此，我们发现二维（2D）YN不仅具有先前报道的面外QAHE，还具有可调谐的面内QAHE。更重要的是，与先前报道的d/f型铁磁体中的面内QAHE不同，我们首次在二维d铁磁体即YN中报道了这种效应。在基态下，YN单层具有半金属能带结构，并在费米能级处表现出六对完全自旋极化的外尔点。当计入自旋轨道耦合时，YN单层可实现多种拓扑相，这取决于磁化方向。在面内磁化下，YN单层呈现外尔态或面内QAHE态。值得注意的是，通过改变面内磁场方向，陈数（±1）和QAHE边缘通道的传播方向可连续切换。当施加面外磁化时，YN单层实现了具有高陈数3的面外QAHE相。YN单层中所有拓扑相的非平凡边缘态均已被明确识别。这项工作表明，二维YN是研究d铁磁体中面内QAHE相的极佳候选材料。
