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U of T and the Discover of Superfluidity
By Allan Griffin

In the preceding article, Prof. J.F. Allen reminiscences about his days as a graduate student in Toronto. Prof. Allen (who was born on May 6, 1908) is one of the most distinguished low temperature physicists of the 20th century. From 1947-1978, he was Professor and Head of the Department of Physics at the University of St. Andrews. Many of you have seen his famous movie on "Superfluid Helium." The tone of the article is characteristic of Jack Allen, who was (and is) famous for his dry wit! In summer visits to St. Andrews in the last decade, I have had the opportunity to talk to Prof. Allen several times. He was always the perfect host, eager to show a Canadian visitor the hidden sights of that beautiful town and University. He also clearly showed a deep love for his days at the University of Toronto.

In this brief commentary, I would like to discuss a little more about the work of Jack Allen and Don Misener in connection with the discovery of superfluidity in liquid Helium. This is mentioned in the last sentence of Prof. Allen's article, work which "yielded a couple of nice papers." To begin with, the fact that U of T was the second laboratory in the world to be able to make liquid He (1923, the thesis project of Gordon Shrum) was not an accident. During World War I, Prof. McLennan and others in the Physics Department did extensive field studies on gas wells all over Canada to find sources of He gas. This was by request of the British Government, because Helium was viewed as safer than Hydrogen for military balloons. As a result, by the early 1920's, Toronto had amassed a large amount of He gas. Prof. Archie Hallett (Professor of Physics at U of T, 1951 to 1977) has recently given to the Department a valuable collection of papers and documents related to this early collaboration between the low temperature and exploration geophysics people at U of T!

In 1935, A.D. Misener (a M.Sc. student at U of T) did the first measurement of the viscosity of liquid Helium below the transition at T = 2.18 K by measuring how a rotating cylinder slowed down. He concluded that the viscosity sharply decreased, but that it was still finite. This pioneering experiment stimulated others to start looking at the flow properties of liquid Helium below the transition. In January of 1938, two one-page papers appeared, side by side, in Nature. One was by P. Kapitza working in Moscow and the other was by Allen and Misener, both then at Cambridge University. Both papers reported experiments showing that liquid Helium could flow through small channels with apparently zero viscosity. This was the discovery of superfluidity! Unfortunately, most of the credit is usually given to Prof. Kapitza (who later received the Nobel prize in physics in 1978).

Kapitza's 1938 Nature article is very critical of the 1935 Toronto work of Misener (published under the name of E.F. Burton, the Director of the Toronto Physics Department). Since the 1960's, however, we have realized that Misener's oscillating cylinder actually measures the reduced "normal fluid" density and is thus direct evidence of the appearance of a irrotational "superfluid" component. Thus, looking back, U of T physics graduate students discovered superfluidity twice, in 1935 (irrotational flow) and in 1938 (zero viscosity)! Sad to say, neither has ever been honored for this work by the University of Toronto, for perhaps the greatest discovery in physics ever made by people from U of T.

This interest in superfluid Helium by U of T physicists has continued. In particular, I mention the important work of A. C. Hollis-Hallett and A.D.B. Woods on the normal fluid viscosity in the 1950's and the classic work of A.D.B. Woods and D.G. Henshaw on the precise determination of the roton dispersion curve using inelastic neutron scattering at Chalk River in the early 1960's. This tradition continues with the recent work by A. Griffin (theory) and A. Steinberg (experiment) related to Bose-condensation of laser-cooled alkali atoms, a superfluid Bose gas which is the precise analogue of superfluid Helium.

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