# Dresden 2020 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 65: Poster Session Topological Topics

### TT 65.29: Poster

### Donnerstag, 19. März 2020, 15:00–19:00, P2/EG

Effects of the classical analog of the spin Berry curvature in adiabatic spin dynamics — •Simon Michel and Michael Potthoff — I. Institute of Theoretical Physics, Department of Physics, Universität Hamburg

We study the real-time dynamics of interacting many-body models consisting of slow and fast degrees of freedom in the adiabatic (Born-Oppenheimer-like) limit where certain topological terms can emerge in the effective equations of motion. In particular, we consider systems of slow classical spins coupled to fast spin or electron degrees of freedom. Using a Lagrangian approach, the fast variables are eliminated via suitable constraints such that one is left with an effective slow spin dynamics. This can be highly anomalous as is known, e.g., for a single classical spin coupled to a fast conduction-electron system, where the spin Berry curvature can lead to a strongly renormalized precession frequency [1].

Here, we study one or more slow classical spins coupled to a fast classical spin system using analytical as well as numerical techniques. For a single slow spin, we recover the anomalous precession [1] found earlier, even quantitatively. However, in the effective equation of motion the (quantum) Berry curvature is replaced by a (classical) topological charge density, similar to a skyrmion density but for skymions living on a product of Bloch spheres rather than in Euclidean space. For two and more slow spins, the geometrical spin torques resulting from the topological charge density give rise to unconventional effective RKKY-type couplings and dynamics.