Electron spin pairing and the phase diagram of high-T-c superconductors

The origin of the instability of the normal state of electrons in the super conducting copper oxides is shown by the K-J model, in which the superexcha nge (K) between local moments and the Kondo exchange (J) between electron a nd local moment are considered. The suppression of superexchange via impuri ty doping may induce effective spin coupling between electrons and triplet pairing (S = 1, S-x = 0). The spin pairing theory explains the phase diagra m of high-T-c superconductors, especially the superconducting transition te mperature T-c, the pseudogap temperature T* and the magnetic crossover temp erature T-n as a function of the doped hole concentration. The universal ex pression for the empirical law of the superconducting transition temperatur e is derived from the theory.