Topological properties of magnons in Ferromagnet-Superconductor heterostructure

Studies of nontrivial band topology of magnon are emerging since they are considered to circumvent the shortcomings of traditional electronic based devices since magnons propagate without Joule heating. Here, we present topological properties of magnons in a ferromagnet-superconductor heterostructure in the presence of a magnetic field. Magnons can propagate in the ferromagnetic thin film while magnetic fields penetrate through the type-II superconducting thin film forming a vortex lattice. We show that the ferromagnetic film influenced by the vortex lattice acts as a magnonic crystal and results in the opening of bandgaps in the spin wave spectrum for a periodic vortex lattice. Our observation supports the closing of band gaps and existence of edge states for finite number of vortices. Furthermore, we calculate the Berry curvature and Chern number for the associated magnon bands to characterize the topological properties of the magnons.