Effective transfer for singlets formed by hole doping in the high-Tc superconductors

Abstract
By comparing the exact results of an extended multiband Hubbard Hamiltonian for Cu2O7 and Cu2O8 clusters to those obtained from an effective single band Hamiltonian, we show that the low energy scale physics is very well described by a t-t′-J model which describes the motion of singlets in an antiferromagnetic background of spins. We obtain values for t, t′ and J for both hole and electron doping and show that these are different. We also study the dispersion relations and density of states within the quasi particle approximation both of which show rather interesting characteristics which could be relevant for high Tc superconductors