Superfluidity: How Quantum Mechanics Became Visible
In December 1937, J.F. Allen and A.D. Misener in Cambridge and simultaneously P. Kapitsa in Moscow discovered the superfluidity of liquid helium. In March 1938, F. London proposed that superfluidity was a consequence of a quantum phenomenon called “Bose-E
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Superfluidity: How Quantum Mechanics Became Visible Sébastien Balibar
6.1
Introduction
Why is it that physicists keep trying to study matter at lower and lower temperature? One likely explanation is that, as temperature goes down, thermal fluctuations progressively vanish so that new phenomena appear as a landscape when clouds go up. When approaching the absolute zero (0 K = −273.15 °C) the behaviour of matter becomes sensitive to minute interactions that would be irrelevant at higher temperature when fluctuations are larger. This is how many new properties of matter have been discovered, not only superfluidity and superconductivity (Mendelssohn 1964; Dahl 1993). In 1908, Kamerlingh Onnes succeeded in liquefying helium gas (Kamerlingh 1908; Delft 2005). This was actually natural helium, which Kamerlingh Onnes obtained by isolating the gas from monazite sand found in North Carolina, through the Office of Commercial Intelligence at Amsterdam where his brother was the director. Nowadays, it comes from oil wells. It contains mostly 4He, which results from the radioactive alpha-decay of Uranium in the Earth. The light isotope 3He was not available in large enough quantities until Tritium, which decays into 3He, was used in the military nuclear industry after World War II. Kamerlingh Onnes wanted to see if it was possible to liquefy the last gas that had not yet been liquefied. The transition from gaseous 4He to liquid 4He occurred at 4.2 K under atmospheric pressure. In 1911 and at the same temperature (4.2 K) he made the major discovery for which he received his Nobel prize, that is the superconductivity of mercury (Kamerlingh Onnes 1911): at low temperature, mercury is a metallic solid and he discovered that its electrical resistance vanishes below 4.2 K.
S. Balibar (*) Laboratoire de Physique Statistique de l’Ecole Normale Supérieure, associé au CNRS, à l’Université Pierre et Marie Curie et à l’Université Denis Diderot, 75231 Paris Cedex 05, France e-mail: [email protected] K. Gavroglu (ed.), History of Artificial Cold, Scientific, Technological and Cultural Issues, Boston Studies in the Philosophy and History of Science 299, DOI 10.1007/978-94-007-7199-4_6, © Springer Science+Business Media Dordrecht 2014
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Fig. 6.1 As shown by these two images from a film by J.F. Allen and J.M.G. Armitage (Allen and Armitage 1982), superfluid helium stops boiling below Tλ . This is due to its large thermal conductivity. The left picture is taken at 2.4 K as indicated by the needle of the thermometer on the left. The right picture is taken just below the lambda transition
In order to reach temperatures lower than 4.2 K, Kamerlingh Onnes simply pumped on liquid helium. This time, one could say that he really entered the era of artificial cold because the lowest temperature in the Universe is that of the cosmic background radiation, now known as 2.7 K (Fixsen 2009). It is only a little further down in temperature – at −2.2 K and in December 1937 – that superfluidity was discovered simultaneously by Allen and
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