Topological Magnons in Kitaev Magnets at High Fields

TL;DR

This paper investigates topological magnon bands in Kitaev magnets under high magnetic fields, revealing chiral edge states arising from non-conserving magnon interactions, with implications for tunable topological phases.

Contribution

It demonstrates the existence of topological magnon bands with chiral edge states in the Kitaev-Heisenberg-$\Gamma$-$\Gamma'$ model under strong magnetic fields, highlighting the role of magnon non-conservation.

Findings

Chiral magnon edge states are present in the polarized phase.

Topological properties are linked to magnon non-conserving terms.

Single particle picture validity is tunable by field strength.

Abstract

We study the Kitaev-Heisenberg-$\Gamma$-$\Gamma'$ model that describes the magnetism in strong spin-orbit coupled honeycomb lattice Mott insulators. In strong $[111]$ magnetic fields that bring the system into the fully polarized paramagnetic phase, we find that the spin wave bands carry nontrivial Chern numbers over large regions of the phase diagram implying the presence of chiral magnon edge states. In contrast to other topological magnon systems, the topological nontriviality of these systems results from the presence of magnon number non-conserving terms in the Hamiltonian. Since the effects of interactions are suppressed by $J/h$, the validity of the single particle picture is tunable making paramagnetic phases particularly suitable for the exploration of this physics. Using time dependent DMRG and interacting spin wave theory, we demonstrate the presence of the chiral edge mode and its evolution with field.