Exchange-driven pairing of delocalized carriers in high-temperature superconductors

A semiquantitative pairing model is derived from the properties of a realistic Hamiltonian for CuO2 sheets. Due to large interactions between oxygen ions, to first-order delocalized carriers pair via localized spin-system holes on the Cu sublattice. The largest carrier-Cu couplings are dynamic exchange processes involving the Cu(d10) and Cu(d8) configurations. Up to carrier concentrations of 3040 %, exchange-mediated attraction overcomes the large carrier Coulomb repulsion, present because of dielectric local screening. The same mechanism is shown to be capable of explaining high-temperature superconductivity in BiO3. The pairing interaction is attractive for triplet and repulsive for singlet s-wave pairs.