What Are Superfluids ?
Superfluids are, like superconductors, related to the behaviour of materials at very low temperatures. Superfluids can only observed at much lower temperatures than superconductors, Helium-4 doesn't display superfluid-behaviour until nearly below 2K. and these temperatures are not easy to reach.
When a material does become a superfluid, it displays some very strange behaviour;
- if it is placed in an open container it will rise up the sides and flow over the top
- if the fluid's container is rotated from stationary, the fluid inside will never move, the viscosity of the liquid is zero, so any part of the liquid or it's container can be moving at any speed without affecting any of the surrounding fluid
- if a light is shone into a beaker of superfluid and there is an exit at the top the fluid will form a fountain and shoot out of the top exit
The Lambda Point
There are other interesting facts about superfluids, the point at which a liquid becomes a superfluid is named the lambda point. This is because at around this area the graph of specific heat capacity against temperature is shaped like the greek letter l.
The relationship at the superfluidity boundary of Helium-4,
between its specific heat capacity and its temperature.
The graph has an asymptote at its lambda point; this is when the atoms are moving slowly enough to form a single energy state, and are then unaffected by other atoms. Above the lambda point the atoms all move about in a disordered way, but below this temperature they all move in an organised way. We can see these effects in Helium-4 becuse it is still a liquid at these low temperatures; most materials solidify above these temperatures.
Page Contributed by John Duffell, Year 13 student 1999-2000