New Critical Behavior.II. XY Antiferromagnet on the Layered-Triangular Lattice

Abstract

Phase transition of the antiferromagnetic plane rotator (XY) 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_κ=0.40±0.04 and γ_κ=0.80±0.08. These exponents satisfy the scaling relations ν_κ=ν and α+2β_κ+γ_κ=2, and the associated crossover exponent, φ_κ=β_κ+γ_κ\simeq1.2, 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.