Chiral coupling of magnons in waveguides

TL;DR

This paper presents a theoretical study of chiral magnon-photon interactions in waveguides, demonstrating how the position of ferromagnets can induce directional coupling and energy transfer, with potential for asymmetric magnon distributions.

Contribution

It introduces a method to tune magnon-photon coupling to be chiral via magnet placement, enabling controlled asymmetric energy transfer in ferromagnetic chains.

Findings

Chiral magnon-photon coupling can be achieved by positioning magnets in the waveguide.

Long chains of magnets can concentrate magnons at one edge due to chirality.

Standing waves with low radiation efficiency are inert to the chirality.

Abstract

We theoretically investigate the collective excitation of multiple (sub)millimeter-sized ferromagnets mediated by waveguide photons. By the position of the magnets in the waveguide, the magnon-photon coupling can be tuned to be chiral, i.e., magnons only couple with photons propagating in one direction, leading to asymmetric transfer of angular momentum and energy between the magnets. A large imbalance in the magnon number distribution over the magnets can be achieved with a long chain of magnets, which concentrate at one edge. The chain also supports standing waves with low radiation efficiency that is inert to the chirality.