Weyl magnons in noncoplanar stacked kagome antiferromagnets

TL;DR

This paper predicts the existence of Weyl magnon nodes in noncoplanar stacked kagome antiferromagnets, which can be experimentally observed through thermal Hall effects and surface magnon arcs, expanding the understanding of topological magnonic systems.

Contribution

It introduces a new class of Weyl magnons arising from scalar spin chirality in noncoplanar antiferromagnets, independent of time-reversal symmetry breaking by magnetic order.

Findings

Weyl magnon nodes occur at the lowest excitation energies.

Presence of topological thermal Hall effect linked to Weyl nodes.

Existence of magnon arc surface states connecting Weyl nodes.

Abstract

Weyl nodes have been experimentally realized in photonic, electronic, and phononic crystals. However, magnonic Weyl nodes are yet to be seen experimentally. In this paper, we propose Weyl magnon nodes in noncoplanar stacked frustrated kagome antiferromagnets, naturally available in various real materials. Most crucially, the Weyl nodes in the current system occur at the lowest excitation and possess a topological (anomalous) thermal Hall effect, therefore they are experimentally accessible at low temperatures due to the population effect of bosonic quasiparticles. In stark contrast to other magnetic systems, the current Weyl nodes do not rely on time-reversal symmetry breaking by the magnetic order. Rather, they result from explicit macroscopically broken time reversal symmetry by the scalar spin chirality of noncoplanar spin textures, and can be generalized to chiral spin liquid states. Moreover, the scalar spin chirality gives a real space Berry curvature which is not available in previously studied magnetic Weyl systems. We show the existence of magnon arc surface states connecting projected Weyl magnon nodes on the surface Brillouin zone. We also uncover the first realization of triply-degenerate nodal magnon point in the non-collinear regime with zero scalar spin chirality.