Major physics breakthrough in understanding supersolidity

Dec 05, 2007

Physicists at the University of Alberta, in Edmonton, Alberta, Canada, have made a major advance in the understanding of what appears to be a new state of matter.

Working in the highly specialized field of quantum fluids and solids, Prof. John Beamish, chair of the Department of Physics, and PhD student James Day, report their findings in a paper to be published in the science journal Nature on Wednesday, Dec. 6, 2007. Beamish and Day are the only researchers in Canada conducting experimental research in this area of fundamental physics.

At very low temperatures, helium gas turns into a liquid. Put under extreme pressure the liquid turns into a solid. Physicists have been manipulating solid helium so they can study its unusual behaviour.

In 2004, a research team at Penn State university in the United States, led by Dr. Moses Chan, electrified the physics world when it announced that it may have discovered an entirely new state of matter – supersolidity. The team made the discovery by cooling solid helium to an extremely low temperature and oscillating the material at different speeds. They found that the particles behaved in a way not seen before, which suggested it might show the “perpetual flow” seen in superfluids like liquid helium.

Day and Dr. Beamish have taken this research a different direction. In an experiment not done before, they cooled the solid helium and manipulated the material another way – by shearing it elastically. In doing so, they found that the solid behaved in an entirely new and unexpected way – it became much stiffer at the lowest temperatures.

“The experimental results from the University of Alberta are remarkable,” Dr. Chan said. “Namely, Professor Beamish and his student James Day found that the shear modulus of solid helium increases by 20% when it is cooled below 0.25K.

“Furthermore, the temperature dependence of the shear modulus seems to track the period change seen in torsional oscillator. It seems the two phenomena are related and probably have the same mechanical origin.

“This is an important breakthrough since the original discovery,” Chan said.

Other physicists around the world are also studying the implications. Through this discovery, Beamish and Day have significantly added to the body of knowledge about the fundamental states of matter allowed by nature.

Source: University of Alberta

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Ragtime
1.2 / 5 (6) Dec 05, 2007
I don't think, the supersolidity really exists, it's rather phenomena simmilar to well known phenomena regelation of ice. The thin wire is able to pass through ice block, because the metal-wire interface remains covered by thin layer of water. Such layer is behaving as a fluid at considerably higher temperature, then the bulk phase. At the case of helium frozen such layer will become superfluous bellow certain temperature, thus mimicking the superfluidity of the bulk phase.

As the evidence can serve the fact, so far only torsional-oscillator experiments with porous Vycor or gold blocks explicitly show a signal %u2013 other studies of direct flow plus neutron and X-ray scattering experiments show no evidence for supersolidity and attempts to look for a thermodynamic signature have so far not been successful.
Ragtime
1.6 / 5 (5) Dec 05, 2007
Note that in the mictures of He3 and He4 just the subtle portion of He3 is able to beat down the superfluidity effect, because the He3 fermions are getting to adhere on the porous surface predominantly.

http://physicswor...int/1528
Ragtime
2 / 5 (4) Dec 05, 2007
Earlier this year, for instance, Reppy repeated Kim and Chan's bulk helium-4 experiment but with samples that were heated and re-frozen extremely rapidly so as to introduce disorder, finding that up to 20% of the solid had become superfluid (Phys. Rev. Lett. 98 175302). However, in the Cornell experiment Reppy and Rittner also found that by maintaining the temperature of the solid helium-4 close to its melting point for several hours and then slowly cooling it down again, they could reduce the supersolid signal to less than 0.05% and even make it disappear completely. Since such "annealing" is expected to reduce the level of imperfection in the solid, this suggested that the observed supersolid behaviour is not a universal property of bulk-solid helium-4 but the result of defects or imperfections in the crystal structure. It's evident, the supersolidity is the superfluidity effect occuring at the surface between crystals.

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