II. Electron-Spin Coupled State in the Superconducting Concentration Region

Abstract

A new theoretical explanation is given for the superconducting state in 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 alternant appearance of low-spin and high-spin states in the presence of a local 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 two groups. On the basis of this new metallic state, the temperature versus hole concentration phase diagram is formed, and, based on this diagram, the openings of the spin gap and a new normal-state energy gap are discussed.