The 3D multi-layered solvable six-vertex model: The phase diagram

An anisotropic statistical model on a cubic lattice consisting of locally interacting six-vertex planes solvable via Bethe ansatz (BA), is studied. Symmetries of BA lead to an infinite hierarchy of possible phases, which is further restricted by numerical simulations. The model is solved for an arbitrary value of the interlayer coupling constant. Resulting is the phase diagram in general three-parameter space. Two new phases of chiral (spiral) character and a new first-order phase transition appear due to the interplane interaction. Exact mapping onto the models with some inhomogeneous sets of interlayer coupling constants is established.