Chapter 4 - The Landau Theory of Phase Transitions: General Concept and Its Microscopic Relation to Mean Field Theory

Abstract

As a parting shot to mean field theory, we take up the Landau theory of phase transitions. This theory in its original formulation does not involve any specific physical models, as has been the case in Chapters 2 and 3, but is based entirely on the concepts of spontaneously broken symmetry and on the corresponding order parameter. It is thus capable of far-ranging generalizations, some of which we consider below. The general transparency of Landau's approach stands in distinct contrast to the mathematical intricacies that await us when we go beyond mean field theory. Also, Landau's approach will be seen to be extremely flexible and therefore worth further study, even if the final results agree only qualitatively, or at best semiquantitatively, with experiment.