Z₂-vortex order of frustrated Heisenberg antiferromagnets in two dimensions

Abstract

We discuss the recent experimental data on various frustrated quasi-twodimensional Heisenberg antiferromagnets from the viewpoint of the Z2-vortex order, which include S=3/2 triangular-lattice antiferromagnet NaCrO2, S=1 triangular-lattice antiferromagnet NiGa2S4, S=1/2 organic triangular-lattice antiferromagnets κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2, and S=1/2 kagome-lattice antiferromagnet volborthite Cu3V2O7(OH)2·2H2O, etc.

Magnetic transition and spin dynamics in the triangular Heisenberg antiferromagnetα-KCrO2

“…27 This T v is predicted to lie slightly below the peak temperature in the heat capacity, T peak . 26 Specifically, quantum Monte Carlo simulations 26 have shown that with this model we should expect T peak = 0.137θ CW and T v = 0.123θ CW for classical Heisenberg triangular AFM lattices, where θ CW is the Curie-Weiss constant extracted from fits of the magnetic susceptibility.…”

“…Below T c , the experimental results are compared to another theoretical description of the triangular lattice system which has been invoked to describe previous μ + SR results, 12,19 known as the spin-gel picture. 26,27 Here it is suggested that vortex excitations and spin freezing provide two length scales which determine the behavior: the vortex correlation length ξ v and spin-wave correlation length ξ sw . The vortex correlation length diverges below a topological critical temperature T v , where Z 2 vortex excitations undergo a binding transition.…”

Kitaev anisotropy induces mesoscopicZ2vortex crystals in frustrated hexagonal antiferromagnets

“…IV B. In contrast to thermally induced defects (Z 2 vortices in the HAF model 9,[30][31][32] , or Z vortices driving Berezinsky-KosterlitzThouless transitions 33 ), the Z 2 vortices are here thus favored by energy and not by entropy.…”

Quantum Oscillations of the Metallic Triangular-Lattice AntiferromagnetPdCrO2

“…Also, the trace of Z 2 vortices near T N were recently suggested in PdCrO 2 from electron spin resonance experiments [27]. The short-range correlations of the local 120 spin structure form a chiral vortex near T N [27,28], which can produce the spin texture with a nonvanishing spin chirality. These results strongly suggest that coupling of the itinerant electrons to the underlying spin texture is essential for the unconventional AHE in PdCrO 2 originating from the field-induced spin chirality of frustrated spins.…”