Correlation Functions and Quasiparticle Interactions in Condensed Matter

This volume contains the proceedings of a NATO Advanced Study Institute devoted to the study of dynamical correlation functions of the form (I) J~e-lwt 6ft T- is an equilibrium average. In equation (1) it is useful to regard the product AB as the product of two operators in cases in which A and B refer to different spatial points in a condensed matter sys tem and/or in which A and B behave dynamically in a quasiharmonic way. In the second case, one has a two quasiparticle correlation function and CAB;AB(w) gives information about quasiparticle inter actions. Condensed matter physics has increasingly turned its attention to correlation functions of this type during the last 15 years, partly because the two point and/or one-particle correlation functions have by now been very thoroughly studied in many cases. The study of four point and/or two quasiparticle correlations has proceeded somewhat independently in several diverse fields of condensed matter physics and it was one purpose of the institute to bring experts from these different fields together to describe the current state of their art to each other and to advanced students.

Contenu
I. General Theory.- Kubo and Zubarev Formulations of Response Theory.- Perturbation Theory of Response Functions.- Renormalization Group Approach to Dynamic Critical Phenomena.- Nonlinear Response Theory.- II. Magnetic Systems.- Magnetic Excitations.- A Green Function Approach to Two-Magnon Light Scattering in Antiferromagnets at T < TN.- Two-Spin Light Scattering in Heisenberg Antiferromagnets.- Two-Magnon Spectra of Ferromagnets.- Light Scattering Determinations of Dynamic Four Point Correlation Functions.- III. Liquids.- Second-Order Light Scattering by Classical Fluids I: Collision Induced Scattering.- Second-Order Light Scattering by Classical Fluids II: Double Light Scattering by Critical Fluids.- Numerical Calculations in Classical Liquids.- Optical Polarization in Molecular Dielectric Liquids.- Rotational Relaxation of Solute Molecules in Dense Noble Gases.- Spinodal Decomposition: An Outline.- Mode Coupling Calculations of Critical Phenomena and Polymer Dynamics.- Two Roton Raman Scattering in Superfluid He4.- Roton Bound States in Liquid 4He.- Integrated Raman Intensity in 4He.- Response Function of the Superconducting Order Parameter.- IV. Phonons.- Second Order Phonon Spectra.- Neutron Scattering and Interactions Between Excitations.- Optical Response of Quantum Crystals.- Anharmonic Interference in Scattering Experiments.- List of Contributors.