Higher-harmonic spin-wave excitation by a superconducting antenna with vortices

Abstract

The interaction between superconductivity and magnetism provides new routes for controlling nonlinear excitations in hybrid systems. While dc-driven Abrikosov vortices (fluxons) are known to interact with spin waves, the ability of confined, nearly harmonic vortex oscillations to generate higher-frequency spin-wave modes remains unexplored. Here, by combining time-dependent Ginzburg--Landau modeling with spectral analysis of the microwave near field, we demonstrate higher-harmonic spin-wave excitation driven by a superconducting microstrip antenna in the Shubnikov phase. Unlike conventional harmonic-generation mechanisms associated with nonlinear magnetization dynamics, the magnetic layer remains a linear receiver, whereas the superconducting antenna generates the nonlinear microwave field. We show that nearly sinusoidal vortex motion and the accompanying redistribution of superconducting screening currents produce higher harmonics that couple to spin-wave modes. This response arises from spatial-to-temporal transduction, whereby harmonic vortex motion and the associated redistribution of screening currents convert a spatially nonuniform magnetic-field profile into higher temporal harmonics. Magnetic flux quanta thus act as active nonlinear elements for frequency conversion, extending the accessible spin-wave frequency range in superconducting--magnonic hybrids.