Topological magnons*

Topological magnons have emerged as a new research area in magnetism and spintronics due to their fundamental interest as well as practical utilities such as back-scattering-free spin-transport channels. In this talk, we will give a pedagogical introduction to various topological phases of magnons and their closely related cousins with a focus on recently discovered two-dimensional (2D) magnets. We will begin by discussing one of the first magnonic topological insulators realized in a honeycomb 2D ferromagnet such as CrI3, which is shown to give rise to the thermal Hall effect via the finite Berry curvature of magnons [1]. Novel ways to manipulate the topological property of magnons in mono- and bilayer 2D magnets [2-4], which is crucial for the practical application of topological magnons in spintronic devices, will be introduced as well. Recently, the field of topological magnons has been expanded into the field of topological bosons beyond simple magnons. As one concrete example, we will introduce a new concept of topologically non-trivial magnon-phonon hybridized mode called a topological magnon-polaron, which can be realized in a 2D ferromagnet [5,6] and antiferromagnet such as MnPS3 [7] via generic magnetoelastic coupling. The topology of magnon-polarons of antiferromagnets differs from the ferromagnetic counterpart in that the former and the latter concern the SU(3) and the SU(2) topology of quasiparticle bands, respectively, showing the richness of the topological physics of magnon-polarons in magnetic systems. The talk will be concluded with a future outlook on the research of topological magnons and beyond.