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Wobbly jelly may open superconductor door


The wobbly jelly has excited physicists because of its superfluid properties (Image: John E. Thomas)

A wobbly 'jelly' of lithium atoms made by U.S. scientists could help overcome a major practical barrier to the study of high-temperature superconductivity.

Joseph Kinast and colleagues from Duke University in Durham, North Carolina, report their research in the current issue of Physical Review Letters.

The researchers created the ultra-cold, cigar shaped jelly by trapping lithium-6 atoms in a vacuum. They then cooled the atoms to near absolute zero and set them vibrating.

The way the lithium atom jelly vibrated suggested it had become a superfluid, a fluid made up of particles that had no viscosity or resistance.

The reason why physicists are interested in this is that these lithium atoms belong to a class of particles called fermions.

Previously, fermions, which are not attracted to each other, have not been known to form superfluids.

Superfluids have been only known to form from the other main class of particles, bosons, which are attracted to each other.

Kinast and colleagues think that when they cooled the lithium atoms they paired up and acted like bosons.

From a practical point of view, the findings may help physicists to better understand the behaviour of other fermionic systems such as superconductors.

In a superconductor, electrons, which are also fermions, pair up and act like bosons in a superfluid; they flow without resistance. High-temperature superconductors could lead to developments such as energy-saving power lines and magnetically levitated trains.

A new type of gas

"This is a very new field; we haven't had ultra-cold fermion gas to play with in physics previously," said physicist Professor Peter Drummond of the University of Queensland.

Drummond said the new system could help overcome a key limitation in studying superconductivity, especially at relatively high temperatures. The new system would also allow scientists to develop a theory for how superconductivity works.

He said it was difficult to manipulate electrons in a solid, and experiments were complicated by the fact that superconductors were usually complex materials that contained many different types of particles.

"Fermions are the most common particle in the Universe and if you can find a clean way to study them, then you can make other scientific developments in other fields," he told ABC Science Online. "This is perhaps the cleanest fermionic system ever made."

Drummond said the lithium jelly might also be useful in fermionic systems other than superconductors.

"It could also be used to model matter under other sorts of extreme conditions such as neutron stars."

Professor Oleg Shuskov of the University of Sydney described the new research as "very interesting physics, exciting physics". But he said he was sceptical there would be any applications.

Neither Shuskov of Drummond believed the lithium fermion gas could be used as a high temperature superconductor because the temperatures required for operating a system like this would be impractically low.

Tags: chemistry, computers-and-technology, physics