2026/07/22 by Yuan Xiao, Rimika Jaiswal, Oleg A. Starykh +1
#cond-mat.str-el
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< gc = 2/π to a chiral phase for g>gc. 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.