Field-dependent magnon dispersions in topological magnet

Recently, the first f-electron skyrmions were reported in three centrosymmetric Gd-based materials including Gd2PdSi3. In contrast to the well known skyrmion materials like MnSi, these f-electron skyrmions do not require inversion symmetry breaking. While the competition of frustrated RKKY exchange, anisotropy or four-spin interactions has been proposed as the driving mechanism behind skyrmion stabilization, a detailed microscopic understanding of the underlying spin interactions has remained elusive, and is a key ingredient to designing centrosymmetric skyrmion materials. Neutron spectroscopy is typically the ideal probe for such investigations, however, the significant neutron absorption of Gd has largely prevented this. We identified the centrosymmetric tetragonal heavy-fermion magnet CeAgBi2 as another f-electron material that hosts skyrmion-lattice order. In our recent neutron diffraction study, we gained conclusive evidence for multiple skyrmion-lattice phases, which coincide with a huge topological Hall effect. We have successfully explored the magnon dispersion in zero-field and now propose to gain insight into the field-dependence within the topologically non-trivial phases. In turn, we will determine the underlying interaction mechanisms that underlie the emergence of skyrmions in CeAgBi2. Our study is of general importance with regard to our understanding of magnetically frustrated f-electron systems as well as topologically non-trivial spin textures.