Other topics

Abstract

There are many topics which we have had to leave untouched in this book, simply to keep it of reasonable length. We have said nothing, for example, about semiconductor devices—p—n junctions, transistors, light-emitting diodes and so on — and nothing about amorphous and liquid metals and semiconductors, where the lack of a regular crystal structure means that Bloch waves and Brillouin zones and well-defined energy bands no longer exist. We have said very little about superconductivity, and nothing about magnetically ordered materials like the ferromagnetic metals and the rare earth metals, in which the electron spins line up cooperatively in various ways. To deal with any of these subjects properly would take another book.