Superconductors and superfluids
This chapter introduces superconductivity and superfluidity, phenomena which are macroscopic and hence amenable to thermodynamics, yet which are quantum in nature—macroscopic quantum phenomena. In 1935 a macroscopic theory was developed by Fritz and Heinz London that accounts for the Meissner effect and which introduces many of the concepts that must be explained by the microscopic theory. What would a rotating superconductor do in the absence of an applied field? As people have just seen, a stationary superconductor in an external field develops a circulating supercurrent that expels the field from the interior of the superconductor. Many properties of Helium can be accounted for by the two-fluid model, without having to delve into a fully quantum-based theory. In the fountain effect, however, the superfluid passing through the capillary moves in the direction of the temperature gradient, from cold to hot.