Magazine article Science News

A Solid like No Other: Frigid, Solid Helium Streams like a Liquid

Magazine article Science News

A Solid like No Other: Frigid, Solid Helium Streams like a Liquid

Article excerpt

Captured within the cavities of a porous glass disk, frozen helium has coalesced into a long-awaited, but never-before-observed, quantum phase of matter, a team of physicists claims. In that extraordinary state, known as a superfluid solid or supersolid, the material is expected to flow like a liquid yet maintain its solid crystal structure, says team leader Moses H.W. Chan of Pennsylvania State University in State College.

Frictionless flow, also known as superfluidity, has previously been observed only in liquids and gases (SN: 10/25/03, p. 2G2). "Now, we're saying that even in a solid we can see it," Chan says. In the Jan. 15 Nature, he and his Penn State colleague Eun-Seong Kim present evidence for what they suspect is the world's first supersolid.

"If this discovery of a supersolid is confirmed, it is a major advance," says John R. Beamish of the University of Alberta in Edmonton in a commentary accompanying the report.

William P. Halperin of Northwestern University in Evanston, Ill., calls the new evidence for supersolidity a "sensational result."

For more than 30 years, theorists have predicted supersolidity, but experimentalists had been unable to demonstrate it. Building on a previous approach, Chan and Kim entered the fray with a device called a torsional oscillator. Basically, it's a squat, cylindrical bob suspended from a hollow copper tube that slowly gyrates back and forth. To explore the behavior of solid helium, the researchers placed inside the oscillator's bob a porous glass disk the diameter of a dime. Then they infiltrated the disk's pores with liquid helium and froze the helium under pressure at temperatures near absolute zero.

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. …

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