Short-wave magnons with multipole spin precession detected in the topological bands of a skyrmion lattice

TL;DR

This study detects intermediate-wavelength magnons with multipole spin precession in skyrmion lattice topological bands, revealing new modes and advancing magnonic device potential at GHz frequencies.

Contribution

It demonstrates the first direct detection of intermediate-wavelength multipole magnons in skyrmion lattices using Brillouin light scattering microscopy.

Findings

Identification of quadrupole and possibly sextupole modes

Detection of magnons with wavevectors around 48 rad/μm

Validation of theoretical predictions with spectral data

Abstract

Topological magnon bands enable uni-directional edge transport without backscattering, enhancing the robustness of magnonic circuits and providing a novel platform for exploring quantum transport phenomena. Magnetic skyrmion lattices, in particular, host a manifold of topological magnon bands with multipole character and non-reciprocal dispersions. These modes have been explored already in the short and long wavelength limit, but previously employed techniques were unable to access intermediate wavelengths comparable to inter-skyrmion distances. Here, we report the detection of such magnons with wavevectors $|{\bf q}|\simeq 48$ rad $\mu$m$^{-1}$ in the metastable skyrmion lattice phase of the bulk chiral magnet Cu$_2$OSeO$_3$ using Brillouin light scattering microscopy. Thanks to its high sensitivity and broad bandwidth various multipole excitation modes could be resolved over a wide magnetic field regime. Besides the known counterclockwise, breathing and clockwise modes with dipole character, quantitative comparison of frequencies and spectral weights to theoretical predictions enabled the additional identification of a quadrupole mode and, possibly, a sextupole mode. Our work highlights the potential of skyrmionic phases for the design of magnonic devices exploiting topological magnon states at GHz frequencies.