Regensburg 2016 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 48: Poster Session II

MA 48.65: Poster

Donnerstag, 10. März 2016, 15:00–18:00, Poster B1

Dynamics of magnetic skyrmions due to phase-space Berry phases — •Robert Bamler and Achim Rosch — University of Cologne, Germany

We derive a theory for the motion of smooth magnetic whirls (skyrmions) the presence of spin-orbit coupling. Our theory predicts previously disregarded forces due to Berry phases in momentum and in mixed position/momentum space.

In magnetic materials without inversion symmetry (chiral magnets), the magnetization can build up smooth whirls (skyrmions). Lately, the manipulation of skyrmions has been of great interest due to potential applications in future magnetic storage devices. A popular model for skyrmion dynamics is the Thiele equation, which describes a gyro-coupling between external forces and the skyrmion velocity. This can be explained by Berry phases in position space. The Thiele equation neglects, however, Berry phases in momentum space, whose importance is demonstrated by the large anomalous Hall signal in, e.g., MnSi.

In our work, we derive an equation of motion for skyrmions that includes all effects due to phase-space Berry phases. Starting from a microscopic model we derive the classical equation of motion for the skyrmion position using a non-equilibrium field theory approach and a gradient expansion. The resulting equation of motion correctly reproduces the known gyro-coupling and predicts additional forces due to electron drag and due to Berry phases in momentum-space and in mixed position/momentum space. We also discuss the coupling of an external electric field to the electric charge of skyrmions.