Project Details
Projekt
Topological magnetization dynamics in skyrmion materials
Applicant
Professor Dr. Markus Garst
Subject Area
Theoretical Condensed Matter Physics
Term
since 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 403030645
Magnetic skyrmions are two-dimensional topological textures of the magnetization. In three-dimensional systems, these textures can extend in the third direction forming skyrmion strings. The non-trivial topology of skyrmion strings strongly influences its magnetization dynamics that is at the focus of this proposal.In the first part, we will consider single skyrmion strings in a field-polarized magnetic background. Such strings possess a Goldstone mode due to translational symmetry breaking. Using non-linear spin wave theory, we will derive analytically the effective low-energy theory of this Goldstone mode including its leading non-linearities. In a previous work, we conjectured the form of this theory on phenomenological grounds using symmetry arguments. Here, we would like to derive it systematically starting from a microscopic theory. The non-linearities of the Goldstone mode are able to stabilize solitary waves that travel along the skyrmion string as we showed previously. An analytical theory is available for these waves which is valid in the asymptotic low-energy limit. The corrections to this limit will be investigated in order to compare with numerical simulations. Furthermore, the influence of spin currents on skyrmion strings will be studied. It will be checked whether longitudinal spin currents are able to trigger a dynamical instability of the skyrmion strings. In the second part, the dynamics of skyrmion lattices will be studied. The spin waves experience an emergent electrodynamics when they traverse such a lattice, which will lead to the formation of magnon Landau levels. It turns out that the emergent magnetic field substantially varies in space giving rise to a spatially oscillating field. This in principle allows for various classical trajectories including runaway orbits that are not localized in space like cyclotron orbits but extend across the whole sample. It will be checked whether such runaway orbits are able to explain the concentration of spectral weight in the spin structure factor that identify effective dispersions in momentum and energy space. In addition, we will systematically study the relation of skyrmion excitations found in cubic chiral magnets and magnetic multilayers. Moreover, we will make predictions for the Brillouin light scattering from skyrmion spin waves.
DFG Programme
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