This book is an introduction to the physics of elementary excitations in condensed matter with emphasis on basic concepts and their mathematical representations. The nature of the book is mainly determined by the fact that it was originally written, in Japanese, as one volume of Iwanami Series of Fundamental Physics supervised by Professor H. Yukawa. Our task was to portray the theory of condensed matter from a unified point of view for the student looking for his own research field and also for more senior readers interested in fundamentals of contemporary physics. As our point of view, we chose the concept of elementary excitation, which we believe to be one of the most fruitful concepts discovered by the quantum theory of matter. The present English edition has been translated by the authors themselves from the second, revised Japanese edition published in 1978, six years after publication of the first edition. In translating, we have introduced no major modifications; only the list of references has been made more suitable to overseas readers. In the English as well as in the Japanese editions, Chaps. 1,4, and part of 6 were written by Nakajima, Chaps. 2, 5, and 7 by Toyozawa, and Chaps. 3 and part of 6 by Abe. Finally we should like to thank Professor P. Fulde for kind help and Dr. H. Lotsch, SpriIiger-Verlag, for patient cooperation in making this English edition a reality.

Synchrotron radiation as a spectroscopic research tool has undergone a most inter esting and astonishing historical development and has now come to the stage of an exciting boom. The machines which produce synchrotron radiation were built and de veloped exclusively for other purposes in the past, namely high-energy physics. At the same time, however, they involuntarily became better and better light sources for the spectral range from the visible to the hard x-ray region. Now we are at the point that the first few storage rings have gone into operation as machines dedicated to synchrotron radiation and several more are in the stage of construction and planning. All this was brought about by the successful research performed during the past fifteen years in which several groups allover the world haVe participated at dif ferent accelerator centers mostly symbiotic with high-energy physics. As it happens with a young and rapidly developing field, the number of reviews and monographs is still minute. The objective of this book is to fill an apparent gap and to provide a sound basis for those who are interested in synchrotron radiation and its applica tions."

Self-Trapped Excitons discusses the structure and evolution of the self-trapped exciton (STE) in a wide range of materials. It includes a comprehensive review of experiments and extensive tables of data. Emphasis is given throughout to the unity of the basic physics underlying various manifestations of self-trapping, with the theory being developed from a localized, atomistic perspective. The topics treated in detail in relation to STE relaxation include spontaneous symmetry breaking, lattice defect formation, radiation damage, and electronic sputtering.