Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Probable Discovery of a New, Supersolid, Phase of Matter


In the Friday 3 September 2004 issue of Science Express, two physicists from Penn State University will announce new experimental evidence for the existence of a new phase of matter, a "supersolid" form of helium-4 with the extraordinary frictionless-flow properties of a superfluid.

"Solid helium-4 appears to behave like a superfluid when it is so cold that the laws of quantum mechanics govern its behavior," says Moses H. W. Chan, Evan Pugh Professor of Physics at Penn State. "One of the most intriguing predictions of the theory of quantum mechanics is the possibility of superfluid behavior in a solid, particularly solid helium-4, and we have strong experimental evidence for this behavior," Chan says.

Chan, and his former student and current postdoctoral associate Eunseong Kim, first announced in the 15 January 2004 issue of the journal Nature their observation of the superfluid-like behavior of solid helium-4, which they had confined in a porous glass with pore diameters of several nanometers. In their current experiment, they observed the same superfluid-like behavior in samples of bulk solid helium without any confining matrix. "Our current experiments with bulk solid helium indicate that the superfluid-like behavior we observed is an intrinsic property of the solid—not the result of confinement in any particular porous medium and not a consequence of the large surface area that accompanies a porous host," Chan explains.

Nobel Laureate Anthony Leggett, who comments on Chan’s discovery in the "Perspectives" section of the journal Science, illustrates the concept of a supersolid by saying, "Imagine you take a small solid body—say a coin—set it on the axis of an old-fashioned gramophone turntable, and set the latter into slow rotation. Then the coin will rotate with the turntable—won’t it? Not if it is made of solid 4-He (helium-4) . . ." Such a failure to rotate is characteristic of a superfluid and is known as "nonclassical rotational inertia," or NCRI. "Leggett says of Chan’s latest research, ". . . the most plausible interpretation, and the one drawn by the authors, is that NCRI is indeed occurring . . ."

As in their earlier experiment, Kim and Chan used a laboratory device called a torsional oscillator, which is like an amusement-park ride for experimental samples that rapidly rotates back and forth, to study the rotational property of solid helium. The helium is contained inside a ring-shaped, or "annular," channel located inside the sample cell. The researchers introduce helium gas into the open annular channel under high pressure via a thin capillary tube. Solid helium forms in the channel when the cell is cooled below -270 Celsius, or 3 degrees above absolute zero, under a pressure that exceeds 26 times the normal atmospheric pressure. Kim and Chan then rotated the sample cell back and forth while cooling it to the lowest temperature.

"Something very unusual occurred when the temperature dropped below one-quarter of a degree above absolute zero," Chan says. "The oscillation rate suddenly became slightly more rapid, as if some of the helium has disappeared or simply was not participating in the torsional motion." Kim and Chan found it easy to confirm that the helium had not disappeared—they just warmed the experimental cell and found the oscillation returned to the same slower rate. "The sensible interpretation of the result is that some of the helium does not participate in the oscillation," Chan explains. "In other words, solid helium does not behave as an ordinary solid, but exhibits nonclassical, or reduced, rotational inertia in the supersolid phase, as described by Tony Leggett."

The researchers conclude that what happened inside the annular channel in their experimental sample cell is that a small fraction—roughly 1.5 percent—of the helium atoms enter into a state of zero friction and that this fraction is no longer coupled to the back-and-forth motion of the sample cell or to the rest of the solid. "This 1.5 percent is the supersolid fraction, and its behavior is identical to that found for liquid helium entering the superfluid phase, except that in liquid helium the superfluid fraction is 100 percent at absolute zero," Chan explains. Kim and Chan found supersolid behavior in 17 different samples of solid helium at pressures ranging from 26 atmospheres up to 66 atmospheres.

"What seems certain is that if the interpretation Kim and Chan give of their raw data is correct (and quite probably even if it is not!), their experiment will force theorists to revise dramatically the generally accepted picture of crystalline solid 4-He," Leggett says.

To understand how a supersolid could exist, you have to imagine the realm of quantum mechanics, the theory that explains many of the properties of matter. In this realm there are different rules for the two categories of particles: fermions and bosons. Fermions include particles like electrons and atoms with an odd mass number, like helium-3. Bosons include atoms with an even mass number, like helium-4. The quantum-mechanical rule for fermions is that they cannot share a quantum state with other particles of their kind, but for bosons there is no limit to the number that can be in the identical quantum state. This talent that bosons have for Rockettes-style coordination leads to the remarkable properties that Chan and Kim discovered in solid helium-4.

"When we go to a low-enough temperature, thermal energy is no longer important and this quantum-mechanical effect becomes very apparent," Chan explains. "In the supersolid phase, the supersolid fraction of the particles are executing Rockettes-style coherent superflow around the annular channel, as viewed by the oscillating sample cell."

Kim and Chan tested their conclusion by performing the experiment again, but this time they built a new sample cell with a barrier in the annular channel, blocking its continuous "racetrack" geometry so that superflow could not take place. "In this experiment, we observed that the decoupling rate, as measured by the change in the oscillation rate, decreased by a factor of 60," Chan reports. "The small residual effect is due to the special property of a superfluid and supersolid known as the irrotational flow effect. What is clear is that superflow is indeed interrupted by the barrier in the annular channel," Chan says.

In addition to Chan’s group, a number of other labs and theoretical groups are gearing up to learn more about the thermodynamic, hydrodynamic, and other properties of supersolid helium-4. "We used to think that a solid could not flow, but now we have discovered that when you cool solid helium to a sufficiently low temperature it can not only flow, but it actually flows without friction," Chan says. "The implication of our research is that we now have to rethink what we mean by a solid."

Chan’s research was supported by the Condensed Matter Physics Program of the National Science Foundation.

Barbara K. Kennedy | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Tune your radio: galaxies sing while forming stars
21.02.2017 | Max-Planck-Institut für Radioastronomie

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>



Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

More VideoLinks >>>