Electron Spin Pairing and Excitations in High-T_cSuperconductors

Effective spin coupling between conduction electrons mediated by local Cu moments in the doped CuO₂ plane may induce the instability of the normal states of conduction electrons and pairing at Cu sites, where the superexchange interaction between local moments influenced by hole doping is found to be Ising-like in recent experiments. By a mean field approach, we show that spin pairing and strong pair-pair interaction in the doped antiferromagnetic ordered Ising-like CuO₂ plane gives rise to high temperature superfluid condensation and the exceptional features of quasi-particle excitation in cuprates such as spin gap, pseudogap, and the linear temperature dependence of resistivity ρ_ab in the normal states.