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arXiv · 2607.20629

Ferromagnetic transition in a chiral spin chain

Yuan Xiao·Rimika Jaiswal·Oleg A. Starykh·Leon Balents
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Abstract

We study the zero-temperature properties of a spin-$1/2$ Heisenberg chain with an additional three-site chiral term of strength $g$. The model is known to be integrable and previous work using Bethe ansatz has identified a phase transition from the usual critical state for $g< g_c = 2/\pi$ to a chiral phase for $g>g_c$. Here we combine analytical and computational approaches to demonstrate that the transition point comprises an unusual Lifshitz transition with dynamical critical exponent $z=3$, and the chiral phase is a partially spin-polarized phase which spontaneously breaks SU(2) symmetry. We derive a strongly interacting chiral boson field theory for the critical point, and show that even its small-momentum, low-energy response is non-trivial. We also determine the universal properties of the chiral phase, and specifically show that it has a simultaneous quadratically dispersing ferromagnetic "magnon" mode coexisting with the power-law singularities and linearly dispersing excitations typical of a Luttinger liquid. Our conclusions are validated using numerics based on matrix product state methods and exact diagonalization.

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Yuan Xiao, Rimika Jaiswal, Oleg A. Starykh, Leon Balents. 2026-07-22. Ferromagnetic transition in a chiral spin chain. https://arxiv.org/abs/2607.20629

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