SKM 2023 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 27: Electron Theory of Magnetism and Correlations

MA 27.2: Vortrag

Mittwoch, 29. März 2023, 09:45–10:00, HSZ 403

Geometrical dynamics of magnetic moments coupled to a correlated antiferromagnet — •David Alan Krüger, Nicolas Lenzing, and Michael Potthoff — Department of Physics, University of Hamburg, Hamburg, Germany

The geometrical spin torque represents an indirect interaction of magnetic moments, which are weakly exchange coupled to a system of itinerant electrons. It originates from a finite spin-Berry curvature, it modifies and adds to the conventional indirect RKKY exchange, and it leads to an anomalous, non-Hamiltonian dynamics of the magnetic moments. We demonstrate that there is an unprecedentedly strong geometrical spin torque in case of an electron system, where correlations cause antiferromagnetic long-range order. The key observation is that the anomalous torque is strongly boosted by low-energy magnon modes emerging in the two-electron spin-excitation spectrum as a necessary consequence of spontaneous spin-rotation symmetry breaking. As long as single- electron excitations are gapped out, the effect is largely universal, i.e., essentially independent of the details of the electronic structure, but decisively dependent on the lattice dimension. Analogous to the reasoning that leads to the Mermin-Wagner theorem, there is a lower critical dimension at and below which the spin-Berry curvature diverges. Our proposal is supported by numerical results obtained by the random-phase approximation and by Holstein-Primakov spin-wave theory for the Hubbard model in the weak- and in the strong-coupling limit, respectively.