Topological magnon nodal-lines and absence of magnon spin Nernst effect in layered collinear antiferromagnets

TL;DR

This paper predicts a topological Dirac nodal line magnonic phase in layered honeycomb antiferromagnets, showing the absence of magnon spin Nernst effect due to symmetry, but reveals a magnetic field can induce a thermal Hall effect.

Contribution

It demonstrates the existence of a symmetry-protected topological magnonic phase in layered antiferromagnets and explains the conditions under which a magnon thermal Hall effect can be observed.

Findings

Magnon spin Nernst effect cancels out in layered honeycomb antiferromagnets.

Symmetry breaking induces Berry curvature and topological magnon bands.

Magnetic field enables a magnon thermal Hall effect in these materials.

Abstract

We propose the existence of a symmetry-protected topological Dirac nodal line (DNL) magnonic phase in layered honeycomb collinear antiferromagnets even in the presence of spin-orbit Dzyaloshinskii-Moriya interaction. We show that the magnon spin Nernst effect, predicted to occur in strictly two-dimensional (2D) honeycomb collinear antiferromagnets cancels out in the layered honeycomb collinear antiferromagnets. In other words, the magnon spin Nernst effect in each 2D antiferromagnetic layer cancels out the succeeding layer. Hence, the Berry curvature vanish in the entire Brillouin zone due to the combination of time-reversal and space-inversion ($\mathcal{PT}$) symmetry. However, upon symmetry breaking by an external magnetic field, we show that a non-vanishing Berry curvature and Chern number protected topological magnon bands are induced in the non-collinear spin structure. This leads to an experimentally accessible magnon thermal Hall effect in the $\mathcal{PT}$ symmetry-broken topological DNL magnonic phase of layered honeycomb antiferromagnets. We propose that the current predicted results can be experimentally investigated in the layered honeycomb antiferromagnets CaMn$_2$Sb$_2$, BaNi$_2$V$_2$O$_8$, and Bi$_3$Mn$_4$O$_{12}$(NO$_3$).