What is theoretical condensed matter physics, and why is it interesting?
Condensed Matter Physics is the study of the structure and behaviour of the matter that makes up most of the usual (and unusual) stuff that surrounds us every day. It is not the study of the very small (particle theory) or of the very large (astrophysics and cosmology) but of the things in between. It takes for granted that most of these are made up of electrons and nuclei interacting according to the well-established laws of electromagnetism and quantum mechanics, and tries to explain their properties. What makes it an interesting and fundamental branch of physics? It turns out that large assemblies of electrons and nuclei in a condensed state often exhibit so-called cooperative behaviour which is quite different from that of the individual parts. Superconductivity, for example. And the study of this new behaviour requires theoretical methods which can be every bit as sophisticated as those of particle theory or relativity. In fact, mathematically they often have a lot in common. But
