Deeply nonlinear magnon-photon hybrid excitation

TL;DR

The paper addresses how deep nonlinear driving affects magnon–photon coupling in a YIG-sphere/SRR hybrid at room temperature. By mapping transmission spectra versus external field and microwave power, the authors show that strong coupling at low power gives way to power-induced damping of magnetostatic modes, and that Suhl’s first-order instability triggers decay into $ extpm k$ magnons below a threshold field, suppressing the coupling. Above the threshold field, the instability is not activated and the modes remain robust, delineating a nonlinear boundary. These findings highlight opportunities to harness nonlinear magnonics for frequency conversion and switching in integrated magnon–photonic devices.

Abstract

We investigate the microwave-power dependence of magnon-photon coupling in a yttrium iron garnet-sphere/split-ring-resonator hybrid system at room temperature and demonstrate that nonlinear spin-wave interactions suppress the coupling through power-induced dissipation of magnetostatic modes. At low microwave power, the modes exhibit pronounced level repulsion, evidencing strong coupling to the microwave field. As the power increases, however, magnon linewidth broadening progressively weakens the coupling and ultimately suppresses it entirely below a threshold external magnetic field. We show that this behavior originates from Suhl's first-order instability: magnetostatic modes, which couple to the resonator, parametrically excites two counter-propagating magnons at half its frequency, causing modes below the threshold external magnetic field to vanish. In contrast, magnon modes above the threshold field remain robust even at high power, as the instability criterion is not satisfied in that regime. These results reveal a well-defined nonlinear boundary for magnon-photon coupled systems and highlight a favorable regime for exploiting nonlinear magnonics for frequency conversion, switching, and other functional magnonic devices.

Figures (3)

• Figure 1: (a) Experimental setup: The split-ring resonator (SRR) is positioned near the microwave feedline, with a YIG sphere placed in the center of the SRR. Transmission spectra are recorded by a VNA as a function of magnetic field and frequency. Schematic illustrations of the three-magnon (b) splitting and (c) confluence processes in which momentum and energy are conserved. YIG sphere spin-wave dispersions at (d) 87 mT and (e) 130 mT, respectively, for propagation angles ranging from $\theta_k = 0$ (black curve) to $\pi/2$ (blue curve). The shaded regions represent intermediate angles. Cyan and magenta dashed lines serve as guides to the eye for the frequencies $\omega_0$ and $\omega_0/2$, respectively. Three magnon splitting is possible at 87 mT, but not at 130 mT. (f) Measured transmission spectra showing the coupling between magnon and the SRR modes at –20 dBm. Overlaid are calculated magnetostatic mode families in the sphere: ($m, m$) modes shown as solid lines and ($m+1, m$) modes as dotted lines. (g) Avoided level crossing corresponding to the (1,1) mode - i.e., Kittel mode - and the SRR mode and a fit to the coupled harmonic oscillator model.
• Figure 2: Experimentally observed microwave-power dependent magnon-photon coupling. (a)-(d) Transmission spectra as a function of magnetic field and microwave frequency at input microwave powers of –20, –5, 0, and +10 dBm, respectively. (e)-(h) Corresponding inverse Fourier transforms of panels (a)-(d). (i)-(l) Rabi-like oscillations at 87 mT extracted from the time-domain data in panels (e–h) -- extracted along the dashed lines.
• Figure 3: (a) The transmission spectra as a function of frequency and microwave power at 114 mT. (b) Lineplots of transmission spectra at 87 mT for various microwave power levels extracted from Fig. \ref{['fig2']}, showing the evolution of resonance features. (c) Transmission spectra lineplots of the magnon mode detuned from the coupling region as a function of external magnetic field at a fixed frequency of 2.4 GHz, presented for different microwave power levels. (d) Transmission spectra as a function of frequency at 114 mT for various microwave power levels, showing no noticeable power dependence in the spectral response—indicating that Suhl’s first-order instability condition is not satisfied. The small kink above 2.55 GHz is from another nearby higher order mode.