New Critical Behavior.II.XYAntiferromagnet on the Layered-Triangular Lattice

Phase transition of the antiferromagnetic plane rotator ( X Y ) model on the ( d =3)-dimensional layered-triangular lattice is studied by means of Monte Carlo simulations. A single continuous transition is observed with the novel critical exponents α=0.40±0.10, β=0.25±0.02, γ=1.10±0.10 and ν=0.53±0.03. The chirality is found to order simultaneously with the spins, the associated chirality exponents being β k =0.40±0.04 and γ k =0.80±0.08. These exponents satisfy the scaling relations ν k =ν and α+2β k +γ k =2, and the associated crossover exponent, φ k =β k +γ k ≃1.2, exceeds the susceptibility exponent γ. Previous Monte Carlo data for the corresponding ( n =3) Heisenberg model are also reanalyzed taking account of the spin-wave correction, to yield the revised estimates of exponents α=0.34±0.10, β=0.28±0.02, γ=1.10±0.10 and ν=0.55±0.03. The Monte Carlo results support the renormalization-group prediction that the critical behavior of these layered-triangular antiferromagnets is governed by a new type of chiral fixed point.