Understanding Some of the Mysteries of Superfluid Helium

Abstract

As early as 1928, the terms “He I” and “He II” were assigned to liquid helium in order to distinguish the thermal and state properties of the liquid above and below the lambda-point temperature, about 2.17 K. In the late 1930s, the discovery of the exceptional mass and thermal transport properties of He II earned the fluid the additional title of “superfluid.” Since then, these transport properties have excited and tantalized some of the world’s foremost experimental and theoretical physicists. Here, brief consideration is given to the early theoretical models of F. London, Tisza, and Landau who attempted to explain such superfluid phenomena as “zero viscosity,” the thermomechanical (fountain) effect, anomalously high thermal conductivity, and superfluid film flow. Superfluid critical velocities and dissipative processes are discussed in terms of Onsager/Feynman vortex line/ring production. Some details are given of narrow-channel isothermal and thermal flow, film-flow, and film thickness experiments conducted at Los Alamos in efforts to elucidate dissipation processes in these systems. Despite the considerable progress made in understanding superfluidity and the causes of its breakdown, much remains to be explored and explained.