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.

The behaviour of electrons in systems without periodicity is one of the most fascinating areas in solid-state physics, and the last 25 years have seen an enormous increase in research in this field. This has given rise to many new ideas for understanding electronic states in disordered systems, especially the study of the degenerate electron gas in which electron-electron interactions are important. This book provides a much needed survey of these advances. In the first part of the book, the authors discuss impurity bands in three dimensions. Attention is focused on the regime in which the electrons are spatially localized rather than free, so that an interesting interplay of localization and interaction arises. In the second part of the book, they look at the outstanding features of the two-dimensional systems, explaining how these make the localization problem special and interesting. The authors have provided a clear outline of the theoretical picture for the chosen materials and description heuristic. Each chapter is self-contained, allowing readers to pursue their special interests.

Since the discovery by Bednorz and Muller of Cu-O alloys displaying high temperature superconductivity, great energy has been put into research in this field. One of the most important and interesting issues, and the subject of this volume, is the clarification of the microscopic origin and mechanism of high temperature superconductivity. This book discusses the latest experimental results on magnetic, optical, electrical, thermal and mechanical properties of the Cu-O and Bi-O superconductors, as well as proposed theoretical models of the mechanisms. The participants in the symposium agreed that for the high Tc Cu-O superconductors electron correlation effects are of central importance. For the Bi-O superconductors the main topic was whether the mechanism of superconductivity is the same as that of high Tc Cu-O superconductors. What was and what was not resolved at the symposium is summarized at the end of the volume.