Integrable chain model with additional staggered model parameter

The generalization of the Yang-Baxter equations (YBE) in the presence of Z(2) grading along both chain and time directions is presented. The XXZ model with staggered disposition along a chain of both, the anisotropy +/-Delta, as well as shifts of the spectral parameters are considered and the corresponding integrable model is constructed. The Hamiltonian of the model is computed in fermionic and spin formulations. It involves three neighbour sire interactions and therefore can be considered as a zigzag ladder model. The algebraic Bethe ansatz technique is applied and the eigenstates, along with eigenvalues of the transfer matrix of the model are found. The model has a free fermionic limit at Delta = 0 and the integrable boundary terms are found in this case. This construction is quite general and can be applied to other known integrable models. (C) 2000 Elsevier Science B.V. All rights reserved.