Exactly solvable discrete BCS - type Hamiltonians and the Six-Vertex   model
  We propose the new family of the exactly solvable discrete state BCS - type Hamiltonians based on its relationship to the six-vertex model in the quasiclassical limit both in the rational and the trigonometric cases. We establish the relation of the BCS Hamiltonian and its eigenfunctions to the form of the monodromy matrix in the F-basis. Using the Algebraic Bethe Ansatz method for the standard BCS model with equal coupling the expression for the general scalar product and the determinant expressions for the physically interesting correlation functions for the finite number of sites which can be used in the numerical and analytical computations are obtained. We also compare the correlators with the results obtained by means of the variational method. 
A.A. Ovchinnikov