Mook Alexander, Henk Jürgen, Mertig Ingrid
Max-Planck-Institut für Mikrostrukturphysik, D-06120 Halle (Saale), Germany.
Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Phys Rev Lett. 2016 Oct 7;117(15):157204. doi: 10.1103/PhysRevLett.117.157204.
The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs of topologically nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out of plane shifts the Weyl points toward the center Γ[over ¯] of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.
具有Dzyaloshinskii-Moriya相互作用的铁磁焦绿石中磁振子的色散关系被证明具有外尔点，即两个具有相反拓扑电荷的磁振子分支的拓扑非平凡交叉对。由于它们的拓扑性质，它们在表面上的投影由磁振子弧连接，从而与电子外尔半金属的费米弧非常相似。除此之外，倒易空间中外尔点的位置可以通过外部磁场进行广泛调节：在表面平面内旋转时，外尔点和磁振子弧也会旋转；将磁场倾斜出平面会使外尔点向表面布里渊区的中心Γ[上加一横]移动。该理论适用于铁磁焦绿石类，即 kagome晶格上拓扑磁振子绝缘体的三维扩展。在本信函中，我们关注(111)表面，确定适用于所考虑自旋模型的已确立铁磁焦绿石的候选材料，并提出检测拓扑特征的实验。
