paper

Cluster mean-field theory study of Heisenberg model on a square lattice

arXiv:1308.2850

Abstract

We study the spin-1/2 - Heisenberg model on a square lattice using the cluster mean-field theory. We find a rapid convergence of phase boundaries with increasing cluster size. By extrapolating the cluster size to infinity, we obtain accurate phase boundaries (between the Nel antiferromagnetic phase and nonmagnetic phase), and (between nonmagnetic phase and the collinear antiferromagnetic phase). The transitions are identified unambiguously as second order at and first order at . At finite temperature, we present a complete phase diagram with stable, meta-stable and unstable states near , being relevant to that of the anisotropic model. The uniform as well as staggered magnetic susceptibilities are also discussed.

15 pages, 8 figures, 1 table

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