# Unconventional Thermal Magnon Hall Effect in a Ferromagnetic Topological Insulator

## TL;DR

This paper theoretically explores the thermal Hall effect of magnons in a ferromagnetic topological insulator with Kekulé-O coupling modulation and Dzyaloshinskii-Moriya interaction, revealing unconventional conductivity behaviors and tunability.

## Contribution

It introduces a strain-induced KOC modulation in a ferromagnetic lattice, identifying four topological phases and predicting unconventional thermal magnon Hall conductivity behaviors.

## Key findings

- Identification of four topological phases based on KOC and DMI.
- Prediction of unconventional thermal Hall conductivity due to Berry curvature.
- Sign changes in conductivity linked to model parameters and band occupation.

## Abstract

We present theoretically the thermal Hall effect of magnons in a ferromagnetic lattice with a Kekul\'e-O coupling (KOC) modulation and a Dzyaloshinskii-Moriya interaction (DMI). Through a strain-based mechanism for inducing the KOC modulation, we identify four topological phases in terms of the KOC parameter and DMI strength. We calculate the thermal magnon Hall conductivity ${\kappa^{xy}}$ at low temperature in each of these phases. We predict an unconventional conductivity due to a non-zero Berry curvature emerging from band proximity effects in the topologically trivial phase. We find sign changes of ${\kappa^{xy}}$ as a function of the model parameters, associated with the local Berry curvature and occupation probability of the bulk bands. Throughout, ${\kappa^{xy}}$ can be easily tuned with external parameters such as the magnetic field and temperature.