Quantum chemical formulation of high-T-C superconductivity

Artikel i vetenskaplig tidskrift, 1999

A detailed understanding of superconductivity in the cuprates is formulated. A cluster model is defined and evaluated by means of the regularized complete active space self-consistent field method. Signatures of local pair-breaking excitations in a low-dispersive oxygen metal band, attenuated by the nearby buffer ions, and nonadiabatically spin-coupled to a disjoint antiferromagnetic band are quantified and proposed to be consistent with the spin−flip signature of high-TC superconductivity in YBa2Cu3O6+x. Critical properties of the scenario are (i) hole-clustering instabilities producing local angular (D-wave) and radial (S-wave) Cooper instabilities and (ii) nonadiabaticity between local hole cluster states and antiferromagnetism. The cuprates are said to belong to a class of superconductors for which the macroscopic ground state is accessed by means of phase coherent hole cluster resonances. This understanding is illustrated by a real-space BCS-like deduction of the superconducting gap. A microscopic understanding of the order parameter symmetry emerges.