Magnon-polaron driven thermal Hall effect in a Heisenberg-Kitaev antiferromagnet

We investigate the thermal Hall effect in the Heisenberg-Kitaev antiferromagnet Na2Co2TeO6, where we observe negative thermal Hall conductivity (THC) with thermal Hall angles up to 2% at low magnetic fields, which changes the sign to positive THC at higher fields. Our theoretical calculations, incorporating spin-lattice coupling, reveal that the quantum-geometric Berry curvature of magnon polarons counteracts the purely magnonic contribution, resulting in a reversed sign and an increased magnitude in THC. This finding emphasizes the significance of spin-lattice coupling in understanding the thermal Hall effect.