Hybrid Plasmon–Magnon Modes

Updated 29 January 2026

Hybrid plasmon–magnon modes are mixed excitations resulting from strong coupling between plasmons and magnons, producing distinctive Rabi splitting and avoided crossings.
They are engineered via magnetic dipole, inverse spin galvanic, and Dzyaloshinskii–Moriya interactions to achieve tunable dispersion and enhanced light–matter interaction.
These modes enable applications in on-chip signal transduction, quantum sensing, and topological transport, paving the way for advanced magnonics and plasmonics technologies.

Hybrid plasmon-magnon modes are collective excitations arising from the strong coupling between plasmonic and magnonic degrees of freedom in hybrid heterostructures and engineered resonators. These modes emerge in quantum and classical systems in which electromagnetic fields associated with plasmons (collective charge oscillations) coherently interact with spin waves (magnons), producing mixed quantum states and distinctive dispersion relations characterized by avoided crossings, Rabi splitting, and topologically nontrivial band structures. Hybridization occurs via magnetic dipole, magnetoelectric (including spin–orbit and inverse spin galvanic effects), or symmetry-driven (e.g., Dzyaloshinskii-Moriya) couplings. The resulting hybrid modes display enhanced tunability, nonreciprocity, and strong light–matter interaction, and they are of central interest for coherent information propagation, on-chip signal transduction, magnonics, quantum sensing, and topological bosonic transport.

1. Theoretical Models and Coupling Mechanisms

The archetypal description of hybrid plasmon–magnon systems is a coupled Hamiltonian in the rotating-wave approximation: $H = H_\text{pl} + H_\text{mag} + H_\text{int}$ where $H_\text{pl} = \hbar\omega_\text{pl} a^\dagger a$ , $H_\text{mag} = \hbar\omega_m b^\dagger b$ , and $H_\text{int} = \hbar g (a b^\dagger + a^\dagger b)$ , with $a(a^\dagger)$ and $b(b^\dagger)$ annihilating (creating) plasmon and magnon excitations of frequencies $\omega_\text{pl}$ and $\omega_m$ respectively, coupled with strength $g$ .

Several mechanisms underlie the interaction:

Magnetic dipole coupling: The magnonic spin (e.g., uniform Kittel mode) interacts with the plasmonic magnetic field via $H_\text{int} = - \mu_0 \int \vec{m}(\vec{r}) \cdot \vec{h}_\text{pl}(\vec{r}) d^3r$ (Xiong et al., 2024).
Inverse spin galvanic effect: The plasmon electric field induces a non-equilibrium spin polarization via spin–orbit coupling, which couples to magnons by exchange interaction (Dyrdał et al., 2022).
Electric field-modulated Dzyaloshinskii-Moriya interaction: Plasmon electric fields modify local DM vectors, generating direct magnon–plasmon hybridization (Rudziński et al., 13 Jun 2025).
Bond polarization in inversion-broken antiferromagnets: Plasmon fields induce electric dipole contributions that couple to the two-magnon continuum (Gunnink et al., 22 Jan 2025).

The coupling strength $g$ typically scales with the overlap integral (magnetic filling factor $\xi$ ), material parameters (e.g., saturation magnetization $M_s$ , gyromagnetic ratio $\gamma$ ), and geometric or field-tuning factors. In planar devices, $g$ is tunable via device geometry, dielectric environment, gate voltage, and spatial positioning (Xiong et al., 2024, Costa et al., 2022).

2. Dispersion Relations and Mode Hybridization

Hybridization manifests as characteristic splits (Rabi or avoided crossings) in the dispersion relations of the coupled system. Diagonalization of the coupled two-mode Hamiltonian produces mixed eigenfrequencies: $\omega_\pm = \frac{\omega_\text{pl} + \omega_m}{2} \pm \frac{1}{2} \sqrt{(\omega_\text{pl} - \omega_m)^2 + 4g^2}$ At resonance ( $\omega_\text{pl} = \omega_m$ ), the splitting is $2g$.

Key observations:

In graphene–ferromagnet or TI–AFM bilayers, anticrossing gaps reach 0.1–0.2 THz, with cooperativity $C = g^2/(\kappa_\text{pl} \kappa_m)$ exceeding unity for high-quality films (Costa et al., 2022, To et al., 2024, To et al., 2022).
Tunability of the branch structure via electrical gating ( $E_F$ ), mechanical separation, or magnetic bias allows dynamic control over hybrid mode position and gap (Costa et al., 2022, To et al., 2024, Xiong et al., 2024).
Multiple hybrid branches arise in complex or tripartite systems (involving phonons, plasmons, and magnons), with mixing coefficients reflecting the degree of hybridization (Pal et al., 2023).

The following summarizes modal structure in representative platforms:

System	Typical $g$	Hybrid mode branches
Spiral LSP–YIG (resonator) (Xiong et al., 2024)	50–115 MHz	Magnon–LSP polaritons, E/B dipole
Graphene–2D FM (Costa et al., 2022)	50–200 GHz	Plasmon–magnon polaritons, Rabi split
TI–AFM Bilayer (To et al., 2024, To et al., 2022)	10–100 GHz	Dirac plasmon-magnon polaritons
2DEG–AFM (continuum) (Gunnink et al., 22 Jan 2025)	5–10 meV	Plasmon–two-magnon continuum
Tripartite Co/Al (Pal et al., 2023)	780 MHz (g_mp)	Three-mode polaritons (magnon/ph/psm)

3. Tunability, Geometry, and Experimental Control

Hybrid plasmon–magnon coupling is highly engineering-driven:

Device geometry: The structure of spiral resonators, arm density, and central disk diameter in LSP devices controls localized field distributions and hence $\xi$ , affecting $g$ (Xiong et al., 2024).
Dielectric and substrate tuning: Permittivity $\epsilon_r$ alters the effective LC balance and photon mode profile, impacting frequency and field concentration.
Electrical gating: In graphene or TMD-based heterostructures, $E_F$ directly tunes plasmon dispersion and mode overlap (Costa et al., 2022, Finnigan et al., 26 Jan 2026).
Mechanical separation: The evanescent decay in $g \propto e^{-kz}$ allows tuning by adjusting the spacer thickness or layer geometry.
Gate–field control in DM-coupled systems: $E_z$ modulates both magnon dispersion and DM-based coupling strength, enabling real-time sweeping of the hybrid gap (Rudziński et al., 13 Jun 2025).
Spin-orbit and symmetry mechanisms: In AFM semiconductors, spin Hall angles and interface conductance introduce additional couplings mediated by spin torque and pumping (Falch et al., 2024).

4. Topological and Quantum Effects

Topological hybrid plasmon–magnon modes arise in systems with band structure engineering and nontrivial Berry curvature:

Topological Chern bands: Phase-wound coupling terms induce nonzero Berry curvature and quantized Chern numbers in bilayer, TMD–ferrimagnet, and skyrmion-crystal platforms (Hirosawa et al., 9 Oct 2025, Finnigan et al., 26 Jan 2026).
Chiral edge modes: Skyrmion crystals and domain walls host counter-propagating, topologically protected edge states with distinct magnonic and plasmonic character.
Anomalous transport: Intrinsic anomalous thermal Hall and spin Nernst effects are predicted, stemming from Berry curvature of the hybrid bands (Hirosawa et al., 9 Oct 2025, Finnigan et al., 26 Jan 2026).
Spectator and interface branches: Three-or-more mode systems can exhibit "spectator" (zero-Chern) and interface-localized modes tied to reversal of magnetic order parameter (Finnigan et al., 26 Jan 2026).

5. Experimental Realization and Observables

The hybridization is observable via sharp spectral features and mode splitting in reflection, transmission, or near-field measurements:

Microwave spectroscopy: Reflection/transmission ( $S_{11}$ , $S_{21}$ ) of spiral LSP–YIG devices reveals avoided crossings and Rabi splitting (Xiong et al., 2024).
THz/FIR ATR and near-field probing: ATR setups with prism coupling probe the hybrid resonance in graphene–FM, TI–AFM stacks (Costa et al., 2022, To et al., 2024).
Brillouin light and EELS: Resolution of magnon-plasmon anticrossings in spectral loss functions (Dyrdał et al., 2022, Gunnink et al., 22 Jan 2025).
Time-resolved MOKE microscopy: Tripartite polaritons and parametric amplification effects in nanodot arrays (Pal et al., 2023).
Tuning parameters: Bias field, gate voltage, layer thickness, and chip size produce significant (non-monotonic) modulation of splitting and cooperativity, with $C\gg 1$ readily achievable (Xiong et al., 2024, To et al., 2024, Jiang et al., 2024).

Recognition criteria for strong coupling include:

Rabi splitting exceeding damping channels
Cooperativity $C$ significantly greater than unity
Anticrossing gap persistence under linewidth broadening and parameter variation

6. Applications and Functional Implications

Hybrid plasmon–magnon modes enable a broad range of functionalities in quantum and classical device settings:

On-chip routing and coherent state transfer: Fast magnon–photon swaps and reconfigurable magnonic circuits (Xiong et al., 2024, Costa et al., 2022)
Electrically tunable THz modulation: Switching and control of THz propagation via gate-tuned hybrid modes in TI–AFM platforms (To et al., 2024, To et al., 2022)
High-resolution sensing: Sub-femtogram magnetic moment detection and label-free biosensing afforded by localized plasmons (Xiong et al., 2024, Jiang et al., 2024)
Signal transduction and nonreciprocity: Field-tunable circulators, isolators, and parametric amplifiers leveraging biased hybrid mode structure (Xiong et al., 2024)
Quantum information processing: Robust zero-temperature coupling to the two-magnon continuum for quantum transduction (Gunnink et al., 22 Jan 2025)
Magneto-photonic integration: Tripartite polaritons open pathways for spin-wave nanophotonics and ultrafast magneto-optical modulators (Pal et al., 2023)
Topological magnon-plasmonics: Intrinsic Hall and spin Nernst transport, chiral edge modes for dissipationless routing (Hirosawa et al., 9 Oct 2025, Finnigan et al., 26 Jan 2026)

7. Outlook and Representative Research Directions

Emergent research focuses on optimization and extension of hybrid plasmon–magnon coupling:

Bandwidth expansion: Spoof surface plasmon polariton platforms support multi-GHz-range hybridization (Jiang et al., 2024)
Room-temperature operation: Strong coupling feasible well above cryogenic thresholds in Rashba–ferrimagnet systems (Finnigan et al., 26 Jan 2026)
Multimode and tripartite platforms: Simultaneous coupling between magnons, plasmons, and phonons underpins new polariton paradigms (Pal et al., 2023)
Non-magnetic control: Gate-voltage, strain, or field modulation as scalable knobs for hybrid transduction in 2D and vdW materials (Rudziński et al., 13 Jun 2025)
Quantum and topological information transfer: Direct strong-coupling at $T=0$ , topologically-protected transport, and anomalous heat/current responses in engineered bands (Gunnink et al., 22 Jan 2025, Hirosawa et al., 9 Oct 2025, Finnigan et al., 26 Jan 2026)
Integration with photonic and spintronic circuits: Active magnonic–plasmonic elements for logic, sensing, and high-speed data transport (To et al., 2024, Costa et al., 2022, Xiong et al., 2024)

Representative recent works include spiral resonator magnonics with spoof LSPs (Xiong et al., 2024); topological magnon–plasmon bilayers (Hirosawa et al., 9 Oct 2025, Finnigan et al., 26 Jan 2026); graphene–FM and TI–AFM heterostructures with gate-controllable hybridization (Costa et al., 2022, To et al., 2024, To et al., 2022); spin–orbit, DM, and inversion-driven coupling mechanisms (Dyrdał et al., 2022, Rudziński et al., 13 Jun 2025, Gunnink et al., 22 Jan 2025); and tripartite phonon–magnon–plasmon polaritons in nanodot arrays (Pal et al., 2023).