Introduction

Abstract

Abstract Quantum fluids and solids play a special role in condensed matter physics and materials science. The many body theory of Fermi and Bose systems was largely developed in the late 1950s and 1960s to describe liquid 3He and 4He at a microscopic level. The concepts of superfluidity in Bose and Fermi systems have been thoroughly explored in liquid 4He and 3He (cf. Lifshitz and Pitaevskii 1980; Vollhardt and Wölfle 1990). This understanding, hard won in quantum fluids, has found wide application across many fields and in more complex quantum systems. Solid helium is the most quantum solid readily available in nature. It displays highly anharmonic dynamics and serves as a prototype for more complex anharmonic solids. The self- consistent phonon theory also found its severest test in solid helium. For these reasons there is a vast literature and many books on this topic. A list of recent titles and conference proceedings appears at the end of this book.