By the Baxter's
Q72-operator method, we demonstrate the equivalent theory between the generalized
τ(2)-model (other than two special cases with a pseudovacuum state) and the
N-state chiral Potts model with two alternating vertical rapidities, where the degenerate models are included. As a consequence, the theory of the XXZ chain model associated to cyclic representations (with the parameter
ς) of
Uq(sl2) with
qN=1 for odd
N is identified with either (for
ςN=1) the chiral Potts model with two superintegrable vertical rapidities, or (for
ςN=1) the degenerate model for the selfdual solution of the star-triangle relation. In all these identifications, the transfer matrices
T,T^ of the chiral Potts model (including the degenerate ones) serve as the
QR,QL-operators of the corresponding
τ(2)-model, so that the functional relations hold as in the solvable
N-state chiral Potts model.
Generalizing the mapping between the Potts model with nearest neighbor interaction and the six-vertex model, we build a family of “fused Potts models” related to the spin k/2 U q su (2) invariant vertex model and quantum spin chain. These Potts models still have variables taking values 1, …,Q[Formula: see text] but they have a set of complicated multispin interactions. The general technique to compute these interactions, the resulting lattice geometry, symmetries, and the detailed examples of k=2, 3 are given. For Q>4, spontaneous magnetizations are computed on the integrable first order phase transition line, generalizing Baxter’s results for k=1. For Q≤4, we discuss the full phase diagram of the spin 1 (k=2) anisotropic and U q su (2) invariant quantum spin chain [it reduces in the limit Q=4 (q=1) to the much studied phase diagram of the isotropic spin 1 quantum spin chain], Several critical lines and massless phases are exhibited. The appropriate generalization of the valence bond state method of Affleck et al. is worked out.