Magnon topology and thermal Hall effect in trimerized triangular lattice antiferromagnet*

Magnon band topology and magnon transverse responses have been studied in two-dimensional magnetisms for the last few years.
The magnon band topology of the most well-known frustrated two-dimensional spin model antiferromagnetic triangular lattice has got less attention than its cousin Kagome systems because of the spin-chirality cancellation which prohibits thermal Hall effect.
In this work, we study the band topology and thermal Hall effect of triangular lattice antiferromagnet with the nearest-neighbor exchange and external field using linear spinwave theory.
We clarify that the effect PT symmetry forces thermal Hall effect in distortion-free triangular lattice antiferromagnets to zero even when a perpendicular external magnetic field is applied.
We show, however, that (anti-)trimerization distortion in antiferromagnetic triangular lattice removes the symmetry and gives nontrivial magnon band topology and the finite thermal Hall effect.
Finally, we estimate the thermal Hall effect of triangular antiferromagnets with such distortions YMnO₃ and LuMnO₃.