SKM 2023 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 23: Poster Magnetism I

MA 23.30: Poster

Dienstag, 28. März 2023, 17:00–19:00, P1

Abelian spin-Berry curvature of the Haldane model and non-Abelian generalisation — •Nicolas Lenzing, Simon Michel, and Michael Potthoff — I. Institute of Theoretical Physics, Department of Physics, University of Hamburg

The feedback of the geometrical Berry phase, accumulated in an electron system, on the slow dynamics of classical degrees of freedom is governed by the Berry curvature. Here, we study local magnetic moments, modelled as classical spins, which are locally exchange coupled to the (spinful) Haldane model. In the emergent equations of motion for the slow classical-spin dynamics there is a an additional anomalous geometrical spin torque, which originates from the corresponding spin-Berry curvature. Due to the explicitly broken time-reversal symmetry, this is nonzero but usually small in a condensed-matter system. We develop the general theory and compute the spin-Berry curvature, mainly in the limit of weak exchange coupling, in various parameter regimes, particularly close to a topological phase transition. The spatial structure of the spin-Berry curvature tensor, its symmetry properties and the distance dependence of its nonlocal elements are discussed. The investigation has been done in the strict adiabatic limit, where one considers the groundstate only, resulting in an Abelian spin-Berry curvature. It is possible to generalise the formalism for a relaxed adiabatic constraint that takes into account a low-energy subspace. This type of subspace arises, for example, in the case of a degenerate groundstate. The spin-Berry curvature corresponding to the subspace is non-Abelian and does not necessarily vanish for time-reversal symmetric systems.