Dipolar spin waves in uniaxial easy-axis antiferromagnets: A natural topological nodal-line semimetal

Jie Liu,Lin Wang,Ka Shen

doi:10.1103/physrevresearch.2.023282

Abstract

The existence of the magnetostatic surface spin waves in ferromagnets, known as Damon-Eshbach mode, was recently demonstrated to originate from the topology of the dipole-dipole interaction. In this work, we study the topological characteristics of magnons in easy-axis antiferromagnets with uniaxial anisotropy. The dipolar spin waves are found to be, driven by the dipole-dipole interaction, in a topological nodal-line semimetal phase, which hosts Damon-Eshbach-type surface modes due to the bulk-edge correspondence. The long wavelength character of dipolar spin waves makes our proposal valid for any natural uniaxial easy-axis antiferromagnet, and thus enriches the candidates of topological magnonic materials. In contrast to the nonreciprocal property in ferromagnetic case, the surface modes with opposite momentum coexist at each surface, but with different chiralities. Such a chirality-momentum or spin-momentum locking, similar to that of electronic surface states in topological insulators, offers the opportunity to design novel chirality-based magnonic devices in antiferromagnets.

Highlights

Topological materials have attracted great interest in the past decade due to their intriguing fundamental properties and promising applications
We show that dipolar spin waves in uniaxial easy-axis AFMs are naturally in a topological nodal-line semimetal phase
We have analyzed the topological nature of magnons in an easy-axis antiferromagnet with uniaxial anisotropy, which is recognized as a topological nodal-line semimetal driven by the dipolar interaction

Summary

INTRODUCTION

Topological materials have attracted great interest in the past decade due to their intriguing fundamental properties and promising applications Related concepts, such as topological insulators [1,2] and Weyl semimetals [3], in electronic materials have recently been introduced into magnonic systems [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. Among the dipolar spin waves in ferromagnets (FMs), on the other hand, there is a special mode, called the Damon-Eshbach mode [23], with a very similar property of localization near the surface. Based on the outstanding properties of the surface modes, we propose a magnonic device to manipulate their chiralities through a magnetic field gradient

TOPOLOGICAL ANALYSIS

Spin-wave spectrum in an antiferromagnetic film

Device design

SUMMARY

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