Effect of next-nearest-neighbour interaction on dx2-y2-wave superconducting phase in 2D t-J model

An exact diagonalization calculation of the t-J model on 2D square cluster has been studied for the ground state properties of HTSC. Effect of next-nearest-neighbour hopping and magnetic(both antiferromagnetic and ferromagnetic) interaction on d(x2-y2)-wave pairing has been shown. Relative strength of the next-nearest-neighbour interaction with respect to that of near-neighbour interaction for the strongest d(x2-y2)-wave pairing has been estimated. A schematic phase diagram is shown. It is shown that a two-sublattice model with antiferromagnetic interaction between them and a small intra-ferromagnetic-type interaction in one sublattice favours d(x2-y2)-wave superconductivity and moderate negative type NNN hopping adds flavours to this phase.