• A. J. Leggett


The original observation of the phenomenon, or more precisely the complex of phenomena, known as “superfluidity” was made simultaneously in liquid 4-He in 1938 by two groups, Kapitza in Moscow and Allen and Misener in Cambridge. It had been known for some years previously that liquid helium (which, until the early 1950s when the light isotope 3-He began to be produced in experimentally useful quantities from nuclear reactors, was synonymous with liquid 4-He) did not freeze under its own vapor pressure down to the lowest attainable temperatures, and during the early-and mid-1930s it had become clear that some peculiar things happened at and below a characteristic temperature (∼2.17 K), which became known as the “lambda temperature.” Stimulated by measurements that seemed to show that below the lambda temperature the heat flow was not simply proportional to the temperature gradient, Allen and Misener, and simultaneously Kapitza, decided to measure the resistance to the flow of liquid helium clamped in narrow channels and subjected to a pressure drop. They found that while the so-called He-I phase, i.e., helium above the lambda temperature, showed a behavior that could be described in terms of a conventional viscosity, below the lambda point (in the so-called He-II phase) the liquid flowed so easily that if the concept of viscosity was applicable at all, it would have to be at least a factor of 1500 smaller than in the He-I phase. It was this anomalous behavior for which Kapitza coined the term “superfluidity.” Actually, as we shall see below, this “ability to flow without apparent friction” in the kind of geometry employed in the Moscow and Oxford experiments, while spectacular, is not the conceptually simplest manifestation of superfluidity.


Cooper Pair Condensate Fraction Bose Statistic Superfluid Component Condensate Wave Function 
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© Springer-Verlag Berlin Heidelberg 1999

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  • A. J. Leggett

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