Physicists have now heard a quantum-mechanical whistle emanating from two reservoirs of liquid helium-4
that were separated by a perforated membrane.
has become a common tool of science and will be used as the coolant fluid in the Large Hadron Collider, a huge particle accelerator being built under the border between France and Switzerland.
As the scientists continued to lower the temperature, they detected signs that at about 175 millikelvins the solid version of the isotope helium-4
stopped being dragged around because of friction with the disk.
Now, researchers in Canada have evidence for the onset of superfluidity in a droplet containing a mere seven atoms of liquid helium-4
The ratio of two helium isotopes, helium-3 and helium-4
, was higher in these fullerenes than in air.
Now, researchers have shown experimentally that superfluidity can occur in a cluster consisting of as few as 60 helium-4
Wyatt of the University of Exeter in England and his colleagues sent phonons--packets of vibrational energy analogous to photons of light--in specific directions through a pool of liquid helium-4
and helium-3 atoms have different magnetic behavior, collisions between surface helium-4
atoms and wandering helium-3 atoms no longer cause the same spin-flipping effect.
In 1985, a group of physicists at Los Alamos began trying Zurek's proposed experiment with liquid helium-4
, a heavy isotope of the element.
In the late 1930s, researchers found that liquefied helium-4
, the most common helium isotope, becomes a superfluid at a temperature of 2.
The two findings, says Tytler, indicate that the universe contains too much ordinary matter to match the primordial abundances of two isotopes, helium-4
and lithium-7, calculated by other researchers.
It correctly predicted that adding atoms of a lighter helium isotope - helium-3 - to a helium-4
film would widen the temperature range over which the intermediate phase is observed.