Magnonic Floquet Quantum Spin Hall Insulator in Bilayer Collinear Antiferromagnets

S. A. Owerre

doi:10.1038/s41598-019-43702-9

Abstract

We study irradiated two-dimensional insulating bilayer honeycomb ferromagnets and antiferromagnets coupled antiferromagnetically with a zero net magnetization. The former is realized in the recently synthesized bilayer honeycomb chromium triiodide CrI3. In both systems, we show that circularly-polarized electric field breaks time-reversal symmetry and induces a dynamical Dzyaloshinskii-Moriya interaction in each honeycomb layer. However, the resulting bilayer antiferromagnetic system still preserves a combination of time-reversal and space-inversion ({bf{P}}{bf{T}}) symmetry. We show that the magnon topology of the bilayer antiferromagnetic system is characterized by a {{bf{Z}}}_{{bf{2}}} Floquet topological invariant. Therefore, the system realizes a magnonic Floquet quantum spin Hall insulator with spin filtered magnon edge states. This leads to a non-vanishing Floquet magnon spin Nernst effect, whereas the Floquet magnon thermal Hall effect vanishes due to {bf{P}}{bf{T}} symmetry. We study the rich {{bf{Z}}}_{{bf{2}}} Floquet topological magnon phase diagram of the system as a function of the light amplitudes and polarizations. We further discuss the great impact of the results on future experimental realizations.

Highlights

In insulating magnets, the quantum theory of magnons dictates that magnons carry a spin magnetic dipole moment and an intrinsic spin of 1, which can be used for dissipationless information processing in the emerging field of magnon spintronics[31,32]
We can see that for a typical light wavelength λ of order 10−8m, the spin magnetic dipole moment gμB carried by magnon in the irradiated magnetic insulators is comparable to the electron charge e
We propose a 2 magnonic Floquet quantum spin Hall insulator in bilayer collinear antiferromagnets with preserves time-reversal and space-inversion (PT) symmetry

Summary

Introduction

The quantum theory of magnons dictates that magnons carry a spin magnetic dipole moment and an intrinsic spin of 1, which can be used for dissipationless information processing in the emerging field of magnon spintronics[31,32]. We propose a 2 magnonic Floquet quantum spin Hall insulator in bilayer collinear antiferromagnets with PT symmetry. DM interaction in each honeycomb layer, but the bilayer antiferromagnetic system preserves PT symmetry, the resulting magnon topology is characterized by a 2 Floquet topological invariant quantity. The consequence of irradiated insulating antiferromagnets is that hopping magnon with spin magnetic dipole moment gμBzwill accumulate the time-dependent version of the Aharanov-Casher phase[33] given by (see Methods)

Results

Conclusion