Spin pairing: the magnetic origin of high-T-c superconductivity

The experimental results accumulated in the past decade such as coexistence of AF ordering and superconducting coherence, spin gap and anomalous Hall effect indicate that spin coupling is of importance to the unconventional p airing mechanism. By taking a quasi-two-dimensional Ising lattice as the ba ckground, we propose a double exchange model, i.e. Kondo exchange J between electrons and local moments and AF superexchange K between local moments. In a proper doping range where the superexchange K is weakened by the doped holes. we show that Kondo scattering yields an effective spin coupling bet ween two electrons nearby a local moment with suppressed AF exchange, The e ffective spin coupling leads to local triplet pairing (S = 1, S-z = 0) in t he Ising lattice plane. The binding energy of the triplet pair increases wi th the increasing doped hole concentration until a maximum is reached. The K-J model explains the existing experimental results for high-T-c copper ox ides. such as the phase diagram, d-wave pairing, short coherent length, spi n gap, pseudogap and the asymmetry of the tunneling conductance. According to our analysis, high-T-c phenomena are essentially magnetic in nature. (C) 2001 Elsevier Science B.V. All rights reserved.