Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Explaining Bizarre Helium 4, a Likely Supersolid

02.11.2009
Writing in the latest issue of Physical Review Letters, theoretical physicists Boris Svistunov and Nikolai Prokofiev of the University of Massachusetts Amherst, with their student Gunes Soyler, propose a new explanation of certain striking properties of solid helium 4.

Suggesting that atoms in a solid can move or be transported through it seems as impossible as using a syringe to inject material into a billiard ball. It shouldn’t work. But it turns out to be possible under certain conditions in super-solid helium, as demonstrated in scientific testing by UMass Amherst experimental physicist Robert Hallock and his doctoral student Michael Ray, in which atoms are added to a solid.

As the theoreticians Svistunov and Prokofiev explain, supersolidity is somewhat analogous to superconductivity, which is the total lack of electrical resistance that occurs in metals held at very low temperatures. This phenomenon is harnessed today in magnetic resonance imaging machines, for example, where superconducting magnets transport an electric charge, that is electrons, without friction.

This same “superflow,” or supersolidity, was first predicted to occur in a non-metal solid in 1969 by several prominent theoretical physicists who said a solid also should conduct its own atoms without friction when held at sufficiently low temperatures. They proposed helium 4 as a candidate element for observing this in the laboratory. Although early experiments failed to support the existence of super transport in a solid, later work in several laboratories reignited interest.

Svistunov says, “We now know for sure that supersolidity does exist in helium 4, although in a form very different from what was expected in the original theoretical work, and with side effects going far beyond mere super transport.” He and colleagues base this confidence on their first-principles studies of regular and disordered solid helium, using a significant advance in computational science called the “worm algorithm” proposed by them in 1998 and recently applied to helium.

It turns out that a key to supersolidity lies in the nature of the solid. As Svistunov explains, “Our simulations clearly show that a perfect helium 4 crystal is not a supersolid. But we find that certain imperfections, called dislocations, have a superfluid core and thus can demonstrate super transport. This is a possibility first envisioned about 20 years ago by Sergey Shevchenko and it was demonstrated by UMass Amherst experimental physicists Robert Hallock and Michael Ray in 2008.”

According to Svistunov and Prokofiev, Hallock and Ray conducted the first and still unique direct experimental observation of super transport in solid helium 4 in an apparatus Svistunov has dubbed the “UMass sandwich.” It has two reservoirs of liquid helium, each connected by a rod of helium-filled porous Vycor glass to a sample of solid helium 4 kept at 459 degrees below zero Fahrenheit and pressurized to 26 atmospheres. The physicists create a temperature gradient of about 3 degrees across each of the Vycor rods, which keeps the two reservoirs liquid while the solid sample remains a cold solid.

At 459 degrees below zero and high pressure, helium normally wants to be solid, but the tiny pores in the Vycor rods allow the helium atoms to remain in the liquid state. The setup prevents atoms from solidifying despite the temperature and pressure and allows liquid-solid contact at the boundary between helium-filled Vycor and the solid helium, Hallock explains.

“We feed some helium atoms into one reservoir, and we then see an increase in pressure in the second reservoir, which is connected to the first only by a pathway through the Vycor rods and solid helium 4. Below a specific temperature we clearly observe that atoms move from one reservoir to the other through the solid helium, but at higher temperatures they do not. The question is how this super transport can happen.”

To date, according to Hallock, the remarkable observations so far rule out many mundane explanations. More importantly, the UMass Amherst experiments so far do not exclude the possibility that something quite remarkable is taking place, as Svistunov and Prokofiev propose. Hallock notes, “Everything observed so far is consistent with Boris and Nikolai’s predictions. While there are more tests to do, so far we have not refuted their ideas.” He adds that even more striking than the supersolidity per se is the so-called effect of giant isochoric, or constant-volume, compressibility that always is present when flow is observed in the experiment.

Basing their theory on first-principles simulations, Prokofiev, Svistunov and colleagues argue that this bizarre effect is due to a synergy between superfluidity in the cores of imperfections known as dislocations and the known ability of dislocations to “climb,” that is, grow under conditions when mass flow is provided to their cores. There are no practical implications of Svistunov and Prokofiev’s numerical model at present, but as Svistunov observes, “Sooner or later a good theory will become practical. And because we’ve used an unbiased, first principles approach, this work is very meaningful for helping us to understand some of the fundamental properties of quantum matter.”

Svistunov, Prokofiev and Soyler collaborated with colleagues at Harvard and the City University of New York on their recent publication.

Boris Svistunov | Newswise Science News
Further information:
http://www.umass.edu

More articles from Physics and Astronomy:

nachricht Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa

nachricht Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik

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: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>