What Is Superfluidity ?
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;
The Lambda Point
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
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