Rehybridization and pairing in the cuprates

The correlation effects associated with the formation of the local Zhang-Rice singlet are shown to lead to a bound pair of holes in a simple three-band cluster model of the cuprates. The symmetry of the pair function is d(x2)-(y2). The attractive interaction is generated by an occupation-dependent hopping integral deriving from the large U-d characteristic of these materials. Upon doping away from the antiferromagnet, this term drives strong Cu 3d-O 2p charge-transfer excitations, which lead to a dramatic rehybridization and resultant reduction in the local kinetic and Coulomb energy.