# Topological Magnon Bands and Unconventional Thermal Hall Effect on the Frustrated Honeycomb and Bilayer Triangular Lattice

## TL;DR

This paper predicts topological magnon bands and a thermal Hall effect in frustrated honeycomb and bilayer triangular antiferromagnets without relying on Dzyaloshinskii-Moriya interaction, due to magnetic-field-induced spin configurations.

## Contribution

It introduces a mechanism for topological magnon features arising from magnetic fields in systems lacking DMI, expanding understanding of topological phenomena in quantum magnets.

## Key findings

- Topological magnon bands predicted without DMI
- Unconventional thermal Hall effect observed
- Magnetic-field-induced non-coplanar spin configurations

## Abstract

In the conventional ferromagnetic systems, topological magnon bands and thermal Hall effect are due to the Dzyaloshinskii-Moriya interaction (DMI). In principle, however, the DMI is either negligible or it is not allowed by symmetry in some quantum magnets. Therefore, we expect that topological magnon features will not be present in those systems. In addition, quantum magnets on the triangular-lattice are not expected to possess topological features as the DMI or spin-chirality cancels out due to equal and opposite contributions from adjacent triangles. Here, however, we predict that the isomorphic frustrated honeycomb-lattice and bilayer triangular-lattice antiferromagnetic system will exhibit topological magnon bands and topological thermal Hall effect in the absence of an intrinsic DMI. These unconventional topological magnon features are present as a result of magnetic-field-induced non-coplanar spin configurations with nonzero scalar spin chirality. The relevance of the results to realistic bilayer triangular antiferromagnetic materials are discussed.