No valid explanation has been found so far

Jun 20, 2007 20:46 GMT  ·  By
Unlike spinning  tea in a cup, oscillating a supersolid crystal liquid helium keeps it rigidly stationary
   Unlike spinning tea in a cup, oscillating a supersolid crystal liquid helium keeps it rigidly stationary

Supersolidity was first predicted in 1969 by the Russian theorists Alexander Andreev and Ilya Liftshitz.

Supersolids are, spatially ordered materials (solids or crystals) with superfluid properties. Along with superfluids, they represent another state of matter, besides the previously known ones: solids, liquids, gases, plasmas, Bose-Einstein condensates, fermionic condensates, liquid crystals, strange matter and quark-gluon plasmas.

In theory, it might be possible to create a supersolid from quantum fluids like helium-4, which means the solid would show a fluid-like frictionless flow of particles. At near absolute zero, some types of matter become superconducting, carrying electric current with absolutely no resistance, and some of them, like helium, become superfluid at this temperature. This means that a droplet of superfluid helium can rotate inside a container forever, as if it were in a vacuum.

Helium does not solidify at absolute zero in ambient conditions due to its zero-point energy. Rather, both helium-3 and helium-4 exist as superfluids, with no measurable viscosity. At 26 atm, helium-4 does solidify, but it was predicted that at higher pressure, it would become a supersolid: a solid with superfluid properties.

It has been proposed that the observed nonclassical rotational inertia (NCRI) in solid helium actually results from the superflow of thin liquid films along interconnected grain boundaries within the sample. Now, a team of US scientists ruled out the would-be explanation.

They found evidence for supersolidity in single crystals of helium-4, thus showing that the phase does not require superfluid grain boundaries to exist, as some had thought and that grain boundaries are not the responsible mechanism.

Supersolids could one day find practical applications, since today superfluids are used in spectroscopic techniques, as a quantum solvent and in high-precision devices, such as gyroscopes, which allow the measurement of some theoretically predicted gravitational effects.

Probably the most unusual application of superfluids is in slowing down the speed of light. In an experiment, performed by Lene Hau, light was passed through a superfluid and found to be slowed to 17 meters per second (normally ~ 300,000,000 meters per second).