January 1938: Discovery of Superfluidity

A superfluid helium fountain

A superfluid helium fountain

When helium-4 is chilled to below about 2.2 K, it starts to behave in some very weird ways. The fluid passes through narrow tubes with almost no friction, and even climbs up walls and overflows its container. Though there were early suggestions of odd behavior, it took 30 years after helium had been liquefied before its superfluidity was discovered.
In 1908, Heike Kamerlingh Onnes first liquefied helium at the University of Leiden in the Netherlands. Soon there were several hints at the strange behavior of liquid helium. By 1924 Onnes had made precise measurements of liquid helium’s density, and found that as the temperature lowers, the density goes through a sharp maximum at about 2.2 K. In 1927 Willem Keesom and Mieczyslaw Wolfke concluded that that liquid helium undergoes a phase transition at about 2.2 K. This temperature is called the lambda point because the graph of specific heat versus temperature resembles the Greek letter lambda. The two phases are called helium I and helium II. Continue reading January 1938: Discovery of Superfluidity