# Dresden 2020 – wissenschaftliches Programm

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# MA: Fachverband Magnetismus

## MA 17: Skyrmions (jointly with MA, O) (joint session TT/MA)

### MA 17.1: Vortrag

### Montag, 16. März 2020, 16:15–16:30, HSZ 304

Quantum skyrmions in a triangular frustrated ferromagnet — •Vivek Lohani^{1}, Ciarán Hickey^{1}, Jan Masell^{1,2}, and Achim Rosch^{1,3} — ^{1}Institute for Theoretical Physics, University of Cologne, Germany — ^{2}RIKEN Center for Emergent Matter Science, Japan — ^{3}Department of Physics, Harvard University, USA

Classically, skyrmions are described as tiny whirls of magnetization possessing a topological winding number. Their dynamics is similar to that of a charge, proportional to the winding number, that is coupled to an effective magnetic field. However, in the limit of small skyrmion size, quantum effects become important. Frustration stabilized skyrmion models − which exhibit degeneracy between classical skyrmions and antiskyrmions, and an additional zero mode, the *helicity* − provide a natural playground to study these quantum effects.

This begs the question − what is a quantum skyrmion? We argue that, in the quantum sector, a skyrmion is defined through the stable bound states of the Hamiltonian. By performing a numerical study, via exact diagonalization, we first demonstrate the existence of quantum skyrmions and identify the associated quantum selection rules. Furthermore, we explore their dynamics through a low energy, phenomenological Hamiltonian spanned by the translational and the helicity modes, wherein the coupling between translations and helicity leads to a rich dynamics. Most interestingly, we incorporate quantum tunneling, and how it breaks the degeneracy in the classical model and allows effective skyrmion charge to flip, thereby leading to a non-trivial bandstructure that is quite sensitive to the spin quantum number.