THEORY OF HIGH-TEMPERATURE SUPERCONDUCTIVITY IN CUPRATES - II - ELECTRON-SPIN COUPLED-STATE IN THE SUPERCONDUCTING CONCENTRATION REGION

A new theoretical explanation is given for the superconducting state i n copper oxides, based on the first principles variational calculation for CuO6 octahedron and CuO5 pyramid. The key feature of the state is the following: A coherent motion of itinerant holes due to the altern ant appearance of low-spin and high-spin states in the presence of a l ocal antiferromagnetic (AF) ordering of the Cu localized spins creates a metallic and superconducting state. This theoretical prediction is supported by very recent neutron inelastic scattering experiments by t wo groups. On the basis of this new metallic state, the temperature ve rsus hole concentration phase diagram is formed, and, based on this di agram, the openings of the spin gap and a new normal-state energy gap are discussed.