Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Probable Discovery of a New, Supersolid, Phase of Matter

03.09.2004


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:
http://www.psu.edu
http://www.science.psu.edu

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

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: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>