Quantum theory of many-body systems

Intended for graduate students in physics and related fields, this text is a self-contained treatment of the physics of many-body systems from the point of view of condensed matter. The approach, quite traditionally, uses the mathematical formalism of quasiparticles and Green's functions. In particular, it covers all the important diagram techniques for normal and superconducting systems, including the zero-temperature perturbation theory, and the Matsubara, Keldysh, and Nambu-Gor'kov formalisms. The book begins by introducing Green's function for one-particle systems (using Feynman path Integrals), general perturbation theory, and second quantization. It then turns to the usual zero-temperature formalism, discussing the properties and physical meaning of Green's function for many-body systems and then developing the diagram techniques of perturbation theory. The theory is extended to finite temperatures, including a discussion of the Matsubara formalism as well as the Keldysh technique for essentially nonequilibrium systems. The final chapter is devoted to applications of the techniques to superconductivity, including discussions of the superconducting phase transition, elementary excitations, transport, Andreev reflection, and Josephson effect. Problems at the end of each chapter help to guide learning and to illustrate the applications of the formalism.