Integrable ladder t-J model with staggered shift of the spectral parameter

The generalization of the Yang-Baxter equations in the presence of Z(2) gra ding along both chain and time directions is presented and an integrable mo del of t-J type with staggered disposition of shifts of the spectral parame ter along the chain is constructed. The Hamiltonian of the model is compute d in the fermionic formulation. It involves three neighbour site interactio ns and therefore can be considered as a zigzag ladder model. The algebraic Bethe ansatz technique is applied and the eigenstates as well as the eigenv alues of the transfer matrix of the model are found. It is argued that in t he thermodynamic limit the lowest energy of the model is formed by the quar ter filling of the states by fermions instead of the usual half filling.