Magnonic triply-degenerate nodal points

TL;DR

This paper introduces the concept of magnonic triply-degenerate nodal points in non-collinear antiferromagnets, revealing unique surface states and the potential for splitting into Weyl points, expanding understanding of bosonic quasiparticles.

Contribution

It generalizes triply-degenerate nodal points to insulating quantum antiferromagnets and demonstrates their properties and transitions, a novel extension in magnonic topological states.

Findings

Existence of magnonic surface states with constant energy contours.

Magnonic triply-degenerate nodal points can split into Weyl points.

Application to both insulating and metallic antiferromagnets.

Abstract

We generalize the concept of triply-degenerate nodal points to non-collinear antiferromagnets. Here, we introduce this concept to insulating quantum antiferromagnets on the decorated honeycomb lattice, with spin-$1$ bosonic quasiparticle excitations known as magnons. We demonstrate the existence of magnonic surface states with constant energy contours that form pairs of magnonic arcs connecting the surface projection of the magnonic triple nodal points. The quasiparticle excitations near the triple nodal points represent three-component bosons beyond that of magnonic Dirac, Weyl, and nodal-line cases. They can be regarded as a direct reflection of the intrinsic spin carried by magnons. Furthermore, we show that the magnonic triple nodal points can split into magnonic Weyl points, as the system transits from a non-collinear spin structure to a noncoplanar one with a nonzero scalar spin chirality. Our results not only apply to insulating antiferromagnets, but also provide a platform to seek for triple nodal points in metallic antiferromagnets.