Slippery Wave Functions V2.01

TL;DR

This paper discusses the quantum theories of superfluids and superconductors, highlighting the historical development, the roles of quasiparticles and condensates, and the overlooked importance of the condensate in understanding these phenomena.

Contribution

It provides a historical and conceptual analysis of the development of quantum theories for superfluidity and superconductivity, emphasizing the partial neglect of the condensate's role by Landau and Bardeen.

Findings

Landau and Bardeen focused on quasiparticles, underestimating the condensate's importance.

Theories of superfluidity and superconductivity are incomplete without considering the condensate.

Post-1950s advances clarified the critical role of the condensate in these phenomena.

Abstract

Superfluids and superconductors are ordinary matter that show a very surprising behavior at low temperatures. As their temperature is reduced, materials of both kinds can abruptly fall into a state in which they will support a persistent, essentially immortal, flow of particles. Unlike anything in classical physics, these flows engender neither friction nor resistance. A major accomplishment of Twentieth Century physics was the development of an understanding of this very surprising behavior via the construction of partially microscopic and partially macroscopic quantum theories of superfluid helium and superconducting metals. Such theories come in two parts: a theory of the motion of particle-like excitations, called quasiparticles, and of the persistent flows itself via a huge coherent excitation, called a condensate. Two people, above all others, were responsible for the construction of the quasiparticle side of the theories of these very special low-temperature behaviors: Lev Landau and John Bardeen. Curiously enough they both partially ignored and partially downplayed the importance of the condensate. In both cases, this neglect of the actual superfluid or superconducting flow interfered with their ability to understand the implications of the theory they had created. They then had difficulty assessing the important advances that occurred immediately after their own great work. Some speculations are offered about the source of this unevenness in the judgments of these two leading scientists.