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MA: Fachverband Magnetismus

MA 59: Magnonics III

MA 59.11: Vortrag

Freitag, 13. März 2026, 12:15–12:30, POT/0361

Second-Chern Topology of 3D Magnon Bands via a Field-Angle Pump — •Nastaran Salehi and Manuel Pereiro — Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden

We present a general framework to realize second-Chern topology in three-dimensional (3D) bosonic Bogoliubov-de Gennes (BdG) bands by augmenting the Brillouin zone with a slow, cyclic control parameter, yielding a 4D manifold T³×S¹. Using the bosonic metric Σ₃ and paraunitary gauge, we define the non-Abelian Berry connection/curvature for isolated positive-norm band bundles and an integer invariant C₂∈Z. We prove that C₂ quantizes an adiabatic transport: across a slab, the pumped conserved quantity (spin for magnons) per 2π cycle is an integer set by C₂, and the corresponding current is proportional to φ. We introduce a stable lattice algorithm, based on Σ₃-polar link variables, that is gauge covariant and robust in the presence of degeneracies. For the sake of concreteness and pedagogical clarity, we carry out the full derivation in a kagome-based 3D magnet, where a field-angle cycle drives a topological spin flow detectable via inverse spin Hall voltages in Pt contacts on opposing faces. Although illustrated for magnons, the construction applies broadly to quadratic bosonic BdG systems, including phononic and photonic analogues.

Keywords: Second-Chern topology; Bosonic Bogoliubov–de Gennes bands; Non-Abelian Berry curvature; Topological magnon transport; Kagome 3D magnet