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The objective of this book is to provide an up-to-date comprehensive descr- tion of the Kamimura Suwa model, which is the ?rst of the present rep- sentative two-component theories in high temperature superconductivity. In 1986 George Bednorz and Karl Alex Muller made the remarkable discovery ofsuperconductivitywithanunbelievinglyhighvalueofT = 35K,bysubs- c 2+ 3+ tuting Ba ions for La ions in the antiferromagnetic insulator La CuO . 2 4 Soon after this discoveryT rose to 90K by synthesizing YBa Cu O with c 2 3 7?? ade?citinoxygen. Furtherexplorationfornewcopperoxidesuperconducting materials with higherT led to the discovery of Bi Sr Ca Cu O, Tl Ba Ca c Cu O and Hg Ba Ca Cu O compounds in subsequent years. The new class of copper oxide compounds mentioned above is called cuprates . At present T = 135K under ambient pressure andT = 164K under 31 GPa observed c c in HgBa Ca Cu O are the highest value so far obtained. The Kamimura 2 2 3 8 Suwa model, which was originally developed in 1993, is a theory of these real copper oxide superconducting materials. Since undoped La CuO is a 2 4 Mott Hubbard antiferromagnetic insulator, its electronic structure can not beexplained bytheordinaryone-electron energybandtheory. Inthiscontext the important role of electron-correlation was pointed out. 2+ On theother hand, ad-hole state in each Cu ion in theligand ?eld with octahedral symmetry is orbitally doubly-degenerate so that it is subject to strong Jahn Teller interaction in La CuO. Asaresult,aCuO octahedron 2 4 6 in La CuO is elongated along thec-axis due to the Jahn Teller distortion.
List of contents
Experimental Results of High Temperature Superconducting Cuprates.- Brief Review of Models of High-Temperature Superconducting Cuprates.- Cluster Models for Hole-Doped CuO6 Octahedron and CuO5 Pyramid.- MCSCF-CI Method: Its Application to a CuO6 Octahedron Embedded in LSCO.- Calculated Results of a Hole-Doped CuO5 Pyramid in YBa2Cu3O7??.- Electronic Structure of a CuO5 Pyramid in Bi2Sr2CaCu2O8+?.- The Kamimura-Suwa (K-S) Model: Electronic Structure of Underdoped Cuprates.- Exact Diagonalization Method to Solve the K-S Hamiltonian.- Mean-Field Approximation for the K-S Hamiltonian.- Calculated Results of Many-Electrons Band Structures and Fermi Surfaces.- Normal State Properties of La2?xSrxCuO4.- Electron-Phonon Interaction and Electron-Phonon Spectral Functions.- Mechanism of High Temperature Superconductivity.
