Chemical analysis of the superconducting cuprates by means of theory

Kapitel i bok, 2000

An atomistic quantum chemical understanding of superconductivity in the cuprates is articulated. A cluster model is formulated and evaluated by means of the regularized complete active space self-consistent field (reg-CASSCF) method. We quantify charge carriers pairing in one band, local antiferromagnetic (AF) order in a second-band and spin-mediated, nonadiabatic coupling between the two disjoint metallic and magnetic degrees of freedom. The latter resonance is pair-breaking, and becomes spin and symmetry allowed by the "simultaneous" spin excitation in the disjoint local magnetic system. If embedded in a (fluctuating) AF background (i.e., below T-SG), long-range phase coherence necessarily results by means of the local magnetic response initiating virtual spin excitations, the absorption of which elsewhere in the material ensures delocalization of the pair amplitudes.