Efficient shift of ferromagnetic resonance by superconductor gating

The proximity effect has long been recognized as the primary driver of static transport behavior in superconductor/ferromagnetic heterostructures, yet the understanding of magnetic dynamics in this context remains limited. Here, we demonstrate a significant shift of ferromagnetic resonance spectra in ferromagnetic films placed between two superconductor gating layers. Through deliberate modifications of the interface structure using various insertion layers, we have determined that the superconducting proximity effect has a minimal impact on the modulation of ferromagnetic resonance characteristics. Instead, our findings strongly support very recent theoretical predictions that emphasize the phenomenon of ultrastrong coupling between Kittel magnons and Cooper pairs arising from the superconducting magnetoelectric effect. We propose that this ultrastrong coupling not only provides a precise method for determining superconducting parameters like the London penetration depth but also lays the foundation for the manipulation of spin waves through superconductors in future magnonic circuits.