Physical Review Letters
Critical frontier of the antiferromagnetic Ising model in a magnetic field: The honeycomb lattice
Fa Yueh Wu, X. N. Wu, Henk W. J. Blöte
Abstract
A closed-form expression is proposed for the critical frontier, or the critical line, of the antiferromagnetic Ising model on the honeycomb lattice in a nonzero external magnetic field. We formulate the Ising model as an 8-vertex model and identify the critical frontier as a locus invariant under a generalized weak-graph transformation. In its simplest form the locus is an expression containing two unknown constants which we determine numerically. The resulting critical frontier lies very close to results of a finite-size analysis.