A solvable six-vertex model with defects

А. А. Овчинников

Atsushi Nakayashiki

Ingo Peschel, Franz S. Rys

Tetsuo Deguchi

This chapter introduces the six-vertex model defined on a two-dimensional square lattice. It describes the model in detail, since it gives an important prototype of many solvable lattice models defined on two-dimensional lattices. The eight-vertex model, which generalizes the six-vertex model directly, may be considered as the most important exactly solvable model in statistical mechanics. The chapter explores some features of the six-vertex model defined on a square lattice. It reviews a method for diagonalizing the transfer matrix, which is called the coordinate Bethe ansatz, and provides the expressions of the free energy per site in the ferroelectric, the antiferroelectric and the disordered phases, respectively. The chapter discusses some mathematical theories associated with integrable models such as the braid group and the quantum groups. It outlines the Ising model, the Potts models and the chiral Potts model and then the eight-vertex model and the interaction-round-a-face models.

R. Z. Bariev, Andreas Klümper, J. Zittartz

Pierluigi Falco

The six-vertex model on a square lattice is "exactly solvable" because an exact formula for the free energy can be obtained by Bethe Ansatz. However, exact formulas for the correlations of local bulk observables, such as the orientation of the arrow at a given edge, are in general not available. In this paper we consider the isotropic "zero-field" six-vertex model at small |Δ|. We derive the large-distance asymptotic formula of the arrow-arrow correlation, which displays a power law decay and an anomalous exponent. Our method is based on an interacting fermions representation of the six-vertex model and does not use any information obtained from the exact solution.