Phase Diagram of S=1/2 Antiferromagnetic Heisenberg Model on a Dimerized Square Lattice

概要

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The ground state energy, the energy gap and the Fourier transform of the staggered spin correlation function S(Q) at zero temperature are investigated for the S=1/2 antiferromagnetic Heisenberg model on a dimerized square lattice with the help of the spin-wave approximations, the second-order perturbation expansion and the quantum Monte Carlo simulations. In contrast to one-dimensional case, the spin gap appears above a finite critical value of the dimerization parameter. δ_c ≃0.303, where the second-order transition takes place. The antiferromagnetic long range order exists below δ_c. The critical exponent of the order parameter in the antiferromagnetically ordered state is estimated by quantum Monte Carlo calculation to be ≃(δ_c-δ)^β with β=0.27±0.04, while the correlation length in the spin gap region is scaled as ≃(δ-δ_c)^<-v> withν=1.36±0.05. All of them are different from the estimates in one-dimension, ν=1 and the spin-wave approximation, β=ν=1. Possible relevance of our result for the spin gap behavior in high-T_C superconductors is also discussed.
社団法人日本物理学会の論文
1993-10-15