Resolving the momentum dependence of the spin waves in the kagome ferromagnet Fe3Sn2

The kagome lattice geometry can give rise to dispersionless spin or electron manifold states, which can develop emergent quantum phases such as the fractional quantum Hall state or unconventional superconductivity. In the metallic kagome ferromagnet Fe3Sn2, we observed a flat spin wave band showing unconventional amplitude in the long wavelength limit. While the energy of the flat band and the dispersion of the acoustic mode follows a simple nearest-neighbor Heisenberg model, another dispersive optic mode, which is also predicted in the model, is not resolved due to the limitation of the resolution. This mode and its amplitude is very important for the comprehensive understanding of the unconventional behavior of the spin waves. Thus, we propose to study the momentum dependence of the spin waves in Fe3Sn2 with high-resolution RIXS. The results will determine the spin Hamiltonian of this material and develop our understanding of the exotic spin and electron states in kagome magnets.