Dresden 2020 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 18: Skyrmions (joint session TT/MA)

TT 18.1: Vortrag

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

Quantum skyrmions in a triangular frustrated ferromagnet — •Vivek Lohani1, Ciarán Hickey1, Jan Masell1,2, and Achim Rosch1,31Institute for Theoretical Physics, University of Cologne, Germany — 2RIKEN Center for Emergent Matter Science, Japan — 3Department 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.

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