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NSF Press Release


Embargoed until 1:00 P.M. EST
NSF PR 04-05 - January 14, 2004

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 M. Mitchell Waldrop

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 Hollis Wickman

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A Possible New Form of "Supersolid" Matter
Frozen helium-4 behaves like a combination of solid and superfluid

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segment from animation showing an oscillating disk of supersolid matter
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The heart of Chan and Kim's experimental apparatus is a disk filled with solid helium-4. To run the experiment, they hang the disk from a stiff rod and oscillate the disk back and forth. By measuring the frequency of oscillation, the scientists detect whether the solid helium-4 behaves like a supersolid.

An oscillating disk of normal matter, for example, behaves as expected: Because the atoms are rigidly linked, they rotate together.

In an oscillating disk of supersolid matter, many of the atoms rotate, but some do not. Instead, those atoms slip through the lattice like a superfluid, with no friction whatsoever, and sit motionless. That reduces the mass of the disk, which allows it to oscillate faster.

This animation has been exaggerated. In fact, the fraction of helium-4 atoms that refuse to rotate is closer to only 1 percent. And the oscillation frequency Chan and Kim measured—how many times the disk changes direction over a period of time—is actually closer to 1000 times per second. The amplitude of the oscillation—the distance the disk moves in either direction—is not much bigger than the width of a single atom.

Credit: Trent L. Schindler / National Science Foundation
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Researchers at the Pennsylvania State University are announcing the possible discovery of an entirely new phase of matter: an ultra-cold, "supersolid" form of helium-4.

Writing in the 15 January 2004 issue of the journal Nature, Penn State physicist Moses H. W. Chan and his graduate student, Eun-Seong Kim, explain that their material is a solid in the sense that all its helium-4 atoms are frozen into a rigid crystal lattice, much like the atoms and molecules in a normal solid such as ice. The difference is that "frozen," in this case, doesn't mean "stationary." Because helium-4 lattice is so very cold, less than one tenth of a degree above absolute zero, the laws of quantum uncertainty take over. In effect, the helium atoms start to behave as if they were both solid and fluid-at the same time. Under the right circumstances, in fact, some fraction of the helium atoms can begin to move through the lattice like a substance known as a "superfluid": a liquid that moves with no friction whatsoever. Thus the name "supersolid."

Chan and Kim's work, which was funded by the National Science Foundation (NSF), is described in a Penn State press release posted on the EurekAlert site. That site has an embargo of 1 pm Eastern time, 14 January 2004. After that time, the release will also be available at

In addition, NSF has prepared an animation that illustrates the basics of Chan and Kim's experimental setup, and the supersolid behavior they believe they have detected.


Principal Investigator: Moses H.W. Chan, (814) 863-2622,

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering, with an annual budget of nearly $5.3 billion. NSF funds reach all 50 states through grants to nearly 2,000 universities and institutions. Each year, NSF receives about 30,000 competitive requests for funding, and makes about 10,000 new funding awards. The NSF also awards over $200 million in professional and service contracts yearly.

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