Skin phase transition of a skyrmion in a ferromagnetic superfluid

Wooyoung Yun; Se Kwon Kim; Hiromitsu Takeuchi

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arXiv · 2610.17796

Skin phase transition of a skyrmion in a ferromagnetic superfluid

Wooyoung Yun·Se Kwon Kim·Hiromitsu Takeuchi

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Abstract

Compared with a scalar Bose-Einstein condensate (BEC), a spinor BEC supports richer phenomena because of its internal spin degrees of freedom, including topological solitons such as domain walls or skyrmions. Here, we theoretically reveal three distinct axisymmetric soliton structures formed as a circular domain wall in a spin-1 BEC, connected within fixed winding numbers. We refer to these structures as the broken-axisymmetry (BA)-skin, antiferromagnetic (AF)-skin and normal-core phases. Their occurrence is controlled by the two dimensionless parameters in the absence of linear Zeeman coefficient $p=0$: $q/μ$, the ratio of the quadratic Zeeman coefficient to the chemical potential, and $c_s/c_n$, the ratio of spin interaction to the density interaction. The BA-skin and AF-skin phases exhibit local easy-plane magnetic order and local easy-plane spin-nematic order, respectively, while the normal-core phase is similar to a doubly quantized vortex analogous to that of a scalar BEC with a density depletion at the center. We obtain semi-analytical estimates of selected transition boundaries separating these phases by analyzing the Bogoliubov-de Gennes equation and also numerically confirm them by solving the Gross-Pitaevskii equation. We estimate the skyrmion radius using a hydrostatic approximation and compare the result with numerical solutions. We envision our results on skyrmions in a spin-1 BEC can trigger further investigation on novel soliton structures in a magnetic superfluid.

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Wooyoung Yun, Se Kwon Kim, Hiromitsu Takeuchi. 2026-10-13. Skin phase transition of a skyrmion in a ferromagnetic superfluid. https://arxiv.org/abs/2610.17796

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