# Magnon-Fluxon interaction in a ferromagnet/superconductor heterostructure

## TL;DR

This paper reports the first experimental observation of magnon-fluxon interactions in a ferromagnet/superconductor heterostructure, revealing tunable magnon band structures and Doppler shifts caused by flux lattice motion.

## Contribution

It provides the first experimental evidence of magnon-fluxon coupling and demonstrates tunable magnon spectra and flux lattice dynamics in ferromagnet/superconductor heterostructures.

## Key findings

- Magnon frequency spectrum shows a Bloch-like band structure.
- Flux lattice motion causes Doppler shifts in spin wave spectra.
- Magnetically tunable magnon band structures observed.

## Abstract

Ferromagnetism and superconductivity are most fundamental phenomena in condensed matter physics. Entailing opposite spin orders, they share an important conceptual similarity: Disturbances in magnetic ordering in magnetic materials can propagate in the form of spin waves (magnons) while magnetic fields penetrate superconductors as a lattice of magnetic flux quanta (fluxons). Despite a rich choice of wave and quantum phenomena predicted, magnon-fluxon coupling has not been observed experimentally so far. Here, we clearly evidence the interaction of spin waves with a flux lattice in ferromagnet/superconductor Py/Nb bilayers. We demonstrate that, in this system, the magnon frequency spectrum exhibits a Bloch-like band structure which can be tuned by the biasing magnetic field. Furthermore, we observe Doppler shifts in the frequency spectra of spin waves scattered on a flux lattice moving under the action of a transport current in the superconductor.