Signature of a Z₂ Vortex in the Dynamical Correlations of the Triangular-Lattice Heisenberg Antiferromagnet

Abstract

Dynamical properties of the classical Heisenberg antiferromagnet on the triangular lattice are investigated by means of a spin-dynamics simulation and an analytical calculation. While the model was suggested to exhibit a topological transition driven by the Z2-vortex bindingunbinding, weakness of the associated thermodynamic singularity has made it difficult to observe the evidence of the Z2 vortex experimentally so far, only some indirect support. Here, we show that the signature of the Z2-vortex excitation and the vortex-induced topological transition can be captured from the dynamical spin correlations. In particular, the dynamical spin structure factor exhibits a characteristic central peak around the Z2-vortex transition, and this central peak will be a fingerprint of the Z2-vortex excitation.

Development of Spin Correlations in the Geometrically Frustrated Triangular-Lattice Heisenberg Antiferromagnet CuCrO2

“…Because the Z 2 -vortex predicted in 2D TLHAs is a vortex of the chirality vectors defined by local 120 • structures, it results in essentially the same behavior as the trimer model when the correlation length is short. Recently, a theoretical study showed that the excitations of the Z 2 -vortex should produce diffuse scattering connecting the K points [9]. Interestingly, the previously predicted Q pattern of the diffuse scattering looks very similar to those in Figs.…”

“…1(h) and 1(i). Furthermore, the Z 2 -vortex shows a crossover to the spin wave correlations as T decreases [9]. A recent electron spin resonance spectroscopy study of ACrO 2 further suggested the existence of the Z 2 -vortices at T > T N [36].…”

“…A powder neutron scattering study showed that the spin correlations induce diffuse quasielastic scattering in this T region [7]. This spin fluctuation is speculated to be an evidence of excitations of Z 2 vortices [8][9][10], although its origin has not yet been identified.…”

“…One of the most fascinating possibilities is to relate the correlation to the formation of the Z 2 -vortex [8][9][10]. Because the Z 2 -vortex predicted in 2D TLHAs is a vortex of the chirality vectors defined by local 120 • structures, it results in essentially the same behavior as the trimer model when the correlation length is short.…”

Deformed triangular lattice antiferromagnets in a magnetic field: Role of spatial anisotropy and Dzyaloshinskii-Moriya interactions

“…It has been suggested 8 that this finite-T feature in fact reflects a nontrivial phase transition associated with binding of Z 2 vortices permitted by the SO(3) structure. At present, our study, which aims to understand the global features of the deformed Heisenberg model at finite T and h, has nothing to add to this interesting issue, [34][35][36][37][38][39] the resolution of which requires more extensive Monte Carlo simulations.…”