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arXiv · 2507.07463

Breakdown of the conventional spin-wave dynamics and its double-constraint modification in the spin-$\mathbf{\frac{1}{2}}$ triangular-prism Heisenberg antiferromagnet

Shoji Yamamoto·Jun Ohara
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Abstract

Spontaneous magnon decays in an $S=\frac{1}{2}$ Heisenberg antiferromagnet on the equilateral triangular prism are investigated in terms of modified magnon Green's functions. In one dimension, the so-called infrared divergence prevents us from calculating any -- whether static or dynamic -- structure factor within the conventional spin-wave theory even at zero temperature. The well-known modified spin-wave theory initiated by Takahashi completely fails to treat anharmonicities to cause transverse-to-longitudinal coupling which are quite characteristic of noncollinear antiferromagnets. We propose imposing a double-constraint condition on spin waves to solve all these difficulties and get a full view of the nonlinear spin-wave dynamics in one-dimensional frustrated noncollinear antiferromagnets. We reveal a novel instability of the single-particle spectrum in the absence of any well-defined magnetically ordered ground state.

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Shoji Yamamoto, Jun Ohara. 2025-07-10. Breakdown of the conventional spin-wave dynamics and its double-constraint modification in the spin-$\mathbf{\frac{1}{2}}$ triangular-prism Heisenberg antiferromagnet. https://doi.org/10.1209/0295-5075%2Fadedaf

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