Low-Energy Excitations in Disordered Solids

The subject of low-energy excitations in glasses has evolved, since they were first noticed 60 years ago in the thermal properties of oxide glasses and polymers, into a multi-focused amalgam that includes a wide range of other materials containing disorder: amorphous semiconductors and metals, poly-crystalline metals, doped-, mixed- and quasi-crystals, surface adsorbates, ... and topics such as dephasing of quantum states and interferometer noise. The structures causing these effects are known in a few cases, but the central mystery remains: what drives their existence and their uniform properties. A fairly simple empirical description serves well to describe but not to explain them in terms of the material's formation dynamics.This book provides a unified, comprehensive description of tunneling systems in disordered solids suitable for graduate students/researchers wishing an introduction to the field. Its focus is on the tunneling systems intrinsic to glassy solids. It describes the experimental observations of 'glassy' properties, develops the basic empirical tunneling model, and shows how it must be extended to account for, for instance, very low or somewhat higher temperatures, or in limited dimensions, and introduces some of the models that attempt to understand these phenomena within a larger context.The elucidation of the basic tunneling model is the core of the book and is worked out in considerable detail. To keep the total within bounds of our expertise and the reader's patience, many related experimental and theoretical developments are only sketched out here; the text is heavily cited to allow readers to follow their specific interests in much more depth.