Perturbative Input-Output Theory of Floquet Cavity Magnonics and Magnon Energy Shifts

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Main Authors: Aguiar, T., de Oliveira, M. C.
Format: Preprint
Published: 2025
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author Aguiar, T.
de Oliveira, M. C.
author_facet Aguiar, T.
de Oliveira, M. C.
contents We develop a perturbative input-output formalism to compute the reflectance and transmittance spectra of cavity magnonics systems subject to a Floquet modulation. The method exploits the strong hierarchy between the magnetic-dipole couplings transverse (drive field) and parallel (modulation field) to the static bias field, which naturally introduces the small parameter $ε= (2Ns)^{-1/2}$ associated with the total spin $Ns$ of the ferromagnet. By organizing the cavity and magnon fields in a systematic expansion in $ε$, we obtain compact analytic expressions for the spectra up to second order. Using these results, we reproduce the characteristic sideband structure observed in recent Floquet cavity electromagnonics experiments. Furthermore, accounting for the Zeeman interaction between the modulation field and the fully polarized ground state - a contribution typically neglected in previous treatments - we predict an additional magnon detuning of approximately $0.8\,\mathrm{GHz}$, independent of both modulation frequency and sample size and determined solely by the spatial volume occupied by the modulation field. This identifies a measurable and previously overlooked shift relevant for the interpretation and design of cavity magnonics experiments.
format Preprint
id arxiv_https___arxiv_org_abs_2512_12103
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Perturbative Input-Output Theory of Floquet Cavity Magnonics and Magnon Energy Shifts
Aguiar, T.
de Oliveira, M. C.
Mesoscale and Nanoscale Physics
Applied Physics
Quantum Physics
We develop a perturbative input-output formalism to compute the reflectance and transmittance spectra of cavity magnonics systems subject to a Floquet modulation. The method exploits the strong hierarchy between the magnetic-dipole couplings transverse (drive field) and parallel (modulation field) to the static bias field, which naturally introduces the small parameter $ε= (2Ns)^{-1/2}$ associated with the total spin $Ns$ of the ferromagnet. By organizing the cavity and magnon fields in a systematic expansion in $ε$, we obtain compact analytic expressions for the spectra up to second order. Using these results, we reproduce the characteristic sideband structure observed in recent Floquet cavity electromagnonics experiments. Furthermore, accounting for the Zeeman interaction between the modulation field and the fully polarized ground state - a contribution typically neglected in previous treatments - we predict an additional magnon detuning of approximately $0.8\,\mathrm{GHz}$, independent of both modulation frequency and sample size and determined solely by the spatial volume occupied by the modulation field. This identifies a measurable and previously overlooked shift relevant for the interpretation and design of cavity magnonics experiments.
title Perturbative Input-Output Theory of Floquet Cavity Magnonics and Magnon Energy Shifts
topic Mesoscale and Nanoscale Physics
Applied Physics
Quantum Physics
url https://arxiv.org/abs/2512.12103