At first glance, the articles in this book may appear to have nothing in common. They cover such seemingly disparate subjects as the properties of small metallic clusters and the behavior of superfluid He3, nuclear physics and organic materials, copper oxides and mag netic resonance. Why have they been brought together, particUlarly in our time of narrow spe cialization? In fact, the properties and effects described in this book touch upon one and the same fundamental phenomenon: pair correlation. Introduced in the theory of superconductivity by J. Bardeen, L. Cooper, and J. Schrieffer (BCS), this effect plays a key role in various Fermi systems. The book consists of several sections. The first chapter is concerned with conven tional and high Tc superconductors. The second chapter describes two relatively young fami lies of superconductors: organics and fullerenes. Chapter III addresses the superfluidity of 3 He • The discovery of this phenomenon in 1971 was a big event in physics and last year was acknowledged by a Nobel prize. This book contains the text of the Nobel lecture. Chapters IV and V are devoted to correlations in finite Fermi systems such as small metallic clusters, C 60 anions, and atomic nuclei. The book thus covers a broad range of problems, illuminating the close ties between various areas of physics.

The structure of matter is intimately related to the fundamental role played by many-fermion systems. The development in the last few decades of the microscopic many-body theory of correlated fermion systems has been a fertile ground not only for spectacular achievements in basic science in various areas of research, but also for technological applications. Among the numerous phenomena discovered and studied in systems of many fermions, one can cite the superconductivity in metals, the superfluidity in 3He, nuclear matter and nuclei, the quantum Hall effect, the giant resonances in nuclei, the Anderson location and the metal-insulator transition, hole and electron diffusion in doped semiconductors, etc. All these phenomena can be understood only in terms of correlations occurring in many-fermion systems, and the formulation of the correct microscopic theory of each phenomenon has marked a milestone in pure science as well as the starting point for the exploitation of its potential technological applications. It is likely that in the future further developments will take place in this field of basic science.The Hispalensis International School is a summer school aimed mainly at young physicists, both theoreticians and experimentalists, engaged in research work at the predoctoral or recent postdoctoral level. The objective of the School provide an opportunity for participants to come into contact with experienced researchers and hear their clear account of the state of the art of many-body theories in nuclear physics, as well as in related fields, and the main future lines of development.

This research monograph offers an introduction to advanced quantum field theoretical techniques for many-particle systems beyond perturbation theory. Several schemes for resummation of the Feynman diagrams are described. The resulting approximations are especially well suited for strongly correlated fermion and boson systems. Also considered is the crossover from BCS superconductivity to Bose--Einstein condensation in fermion systems with strong attractive interaction. In particular, a field theoretic formulation of "bosonization" is presented; it is published here for the first time. This method is applied to the fractional quantum Hall effect, to the Coulomb plasma, and to several exactly solvable models.