Topological magnon modes on honeycomb lattice with coupling textures

Abstract

Topological magnon modes are expected to be useful for novel applications such as robust information propagation, since they are immune to backscattering and robust against disorder. Although there are several theoretical proposals for topological magnon modes and growing experimental efforts for realizing them by now, it is still desirable to add complementary insights on this important phenomenon. Here, we propose a new scheme to achieve topological magnon where only nearest-neighbour exchange couplings on honeycomb lattice are necessary. In both ferromagnets and antiferromagnets, tuning exchange couplings between and inside hexagonal unit cells induces a topological state accompanied by a band inversion between p-orbital and d-orbital like magnon modes. Topological magnon modes appear at the interface between a topological domain and a trivial domain with magnon currents, which counterpropagate depending on pseudospins originated from orbital angular momenta of magnon modes. This mimics the spin-momentum locking phenomenon in the quantum spin Hall effect.

1D Photonic Topological Insulators Composed of Split Ring Resonators: A Mini Review

“…[95] In particular, the angular momentum of the wave function plays the role of the pseudospin. [94] Based on this pioneering theoretical work, extended theoretical analyses [96][97][98][99][100][101] and experimental demonstrations [102][103][104][105][106] have been conducted. Considering the miniaturization and integration of topological devices, particles (finite crystals) [107] and membrane PCs [108] have been proposed.…”

Magnon Orbital Nernst Effect in Honeycomb Antiferromagnets without Spin–Orbit Coupling

“…40−42 Furthermore, inspired by achievements in topological metamaterials, 43−45 topological magnonic modes carrying the magnon current circulation have been demonstrated in honeycomb magnets with exchange-interaction modulation. 46 However, despite the strong interest in magnon orbitals, studies on their transport properties are very limited. 39,40 For example, the magnon orbital magnetic moment discussed in ref In this work, we answer the question by investigating the transport of magnon orbital moments, which we define as L ̂= 1/4(r × v − v × r) analogously to the modern theory of electron orbital magnetization.…”

“…For example, the circulating magnonic modes have been investigated in confined geometries such as whispering gallery mode cavities, − magnetic nanocylinders and nanotubes. − Also, the orbital magnetization of magnons has been pointed out as the origin of weak ferromagnetism in a noncollinear kagome antiferromagnet (AFM) with the DMI . Recently, the orbital-angular-momentum textures of the magnon bands have been realized in collinear magnets with nontrivial networks of exchange interaction. − Furthermore, inspired by achievements in topological metamaterials, − topological magnonic modes carrying the magnon current circulation have been demonstrated in honeycomb magnets with exchange-interaction modulation . However, despite the strong interest in magnon orbitals, studies on their transport properties are very limited. , For example, the magnon orbital magnetic moment discussed in ref is brought about by spin–orbit coupling (DMI) and therefore its physical manifestations are bound to be weak.…”