XXZ MODEL AS AN EFFECTIVE HAMILTONIAN FOR GENERALIZED HUBBARD MODELS WITH BROKEN ETA-SYMMETRY

We consider the limit of strong Coulomb attraction for generalized Hub bard models with eta-symmetry. In this limit these models are equivale nt to the ferromagnetic spin-1/2 Heisenberg quantum spin chain. In ord er to study the behaviour of the superconducting phase in the electron ic model under perturbations which break the eta-symmetry we investiga te the ground state of the ferromagnetic non-critical XXZ-chain in the sector with fixed magnetization. It turns out to be a large bound sta te of N magnons. We find that the perturbations considered here lead t o the disappearance of the off-diagonal longe-range order.