Multi-magnon Floquet topological chiral edge states

We show that periodic modulation of material parameters (exchange couplings) can induce robust topological multi-magnon edge states that are not present in the static system. This broadens the range of materials which can host topologically protected edge modes, characteristic of topological magnon insulators. Topological magnon insulators are two-dimensional systems with an ordered magnetic ground state and gapped bosonic magnetic excitations (magnons). Robust topologically protected magnon edge states are present when the magnon band structure is nontrivial and the spectrum is gapped. Magnetic systems with Ising anisotropy support two-magnon bound states that are separated in energy from the two-magnon continuum. In the presence of Dzyaloshinkii-Moriya interactions (DMI) the bands have non-trivial topology in the static case (without periodic modulation) [1]. Periodic modulation of the DMI allows us to induce a spectral gap and therefore improve the robustness of the chiral edge states.

[1] A. Mook, R. Hoyer, J. Klinovaja, and D. Loss, Phys. Rev. B 107, 064429 (2023).