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arXiv · 2506.16818

Effective Field Theory of a Noncollinear Altermagnet

Seungho Lee·Se Kwon Kim
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Abstract

We derive an effective field theory for a noncollinear altermagnet and magnons on top of the noncollinear ground state from an altermagnetic Heisenberg model. We obtain the ground-state phase diagram, revealing a noncollinear phase and four distinct collinear phases. The ground state of the noncollinear phase fully breaks the spin rotational symmetry, while the ground state of the collinear phases possesses unbroken $\mathrm{SO}(2)$ symmetry. The resulting effective field theory for the noncollinear phase is an $\mathrm{SO}(3)$ sigma model in which the magnonic excitation has three independent degrees of freedom and exhibits the $d$-wave-like anisotropic linear dispersion. We also discuss possible topological solitons, including $\mathbb{Z}_2$ vortices.

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Seungho Lee, Se Kwon Kim. 2025-06-20. Effective Field Theory of a Noncollinear Altermagnet. https://arxiv.org/abs/2506.16818

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