Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

High-quality helium crystals show supersolid behavior

19.02.2007
High-quality, single-crystal, ultra-cold solid helium exhibits supersolid behavior, suggesting that this frictionless solid flow is not a consequence of defects and grain boundaries in poor-quality, polycrystalline, solid helium, according to a team of Penn State researchers.

In 2004, Penn state physicists -- Eunseong Kim, then-graduate student and Moses Chan, the Evan Pugh professor of physics-- announced the observance of frictionless superflow in solid helium at nearly absolute zero. This new phenomenon is a cousin of Bose-Einstein condensate observed in gases in 1995 and in liquid helium in 1938.

Since then, their results have been replicated at the University of Tokyo, Keio University, Japan, and Cornell University. While the experiment was duplicated at Cornell, one experiment there found that if the solid helium was annealed – cooled slowly from the melting point – the supersolid behavior disappeared. This suggested that the theoretical idea of supersolidity is possible only in poor-quality solid helium and that the superflow is due to defects in the poorly grown crystals.

To create solid helium, the gaseous helium must be cooled very close to absolute zero and put under at least 25 atmospheres. Unlike other gases, helium remains a liquid at ambient pressure all the way down to absolute zero. Determining that the solid helium acts as a supersolid or Bose Einstein condensate is tricky. In a Bose-Einstein condensate all the atoms are at the lowest possible energy state, and they all behave in unison. The supersolid portion of the crystalized helium appears to flow without friction. For liquids and gases, this idea is less difficult because the atoms of both move around more and can easily slide past each other. But, in a solid, especially a very cold one, atoms do not usually flow easily or without friction.

The researchers relied on inertia to determine that the ultra-cold solid helium had a supersolid component. They did the high-pressure cooling experiment in a tiny torsional oscillator, a pendulum-like setup. Liquid helium, under pressure, entered a small chamber at the end of a thin rod. The liquid then cooled to the solid phase and the torsional oscillator was set at a specific frequency.

With a normal solid, the total mass of the sample would dictate the force required to move the oscillator at a specific frequency and as long as the mass remained the same, the same force would be required to keep the system at the same frequency . In Chan and Kim's experiment, when the temperature went below 0.2 degrees Kelvin, the frequency abruptly increased, indicating that some of the solid helium was not moving with the chamber or with the rest of the solid. "At about 25 atmospheres, the initial pressure we investigated, 1 percent of the helium becomes a supersolid," says Chan. "This supersolid fraction becomes frictionless, allowing the rest of the helium to 'flow' past it."

Cornell, in duplicating this experiment used multiple experimental cells, and in one, the annealing process eliminated the supersolid effect. Tony Clark, graduate student in physics is following up on Kim's experiment to test the Cornell findings.

"All solid samples studied to date were made by the so-called blocked capillary method which tends to make poor quality crystals," says Kim. Clark made a new torsional oscillator that allows the growth of solid helium of extremely high crystallinity. The new solid helium is grown from the superfluid phase by keeping the sample cell at the temperature and pressure boundary where both solid and liquid helium coexist. As more helium is very slowly fed into the chamber, a helium crystal grows from the superfluid.

"This constant pressure growth is indeed the preferred method of many prior experiments in growing single crystals," says Chan.

These high quality crystals do exhibit supersolid response, but the supersolid percentage is smaller at only about .3 percent rather than 1 percent.

In another experiment, Chan's team tested the expected result of increased pressure on the solid helium to determine the pressure at which supersolid behavior disappears. Kim and Chan extended the experiment up to 130 atmospheres and found the supersolid portion decreases with pressure from 60 atmospheres and higher. The researchers extrapolated the decreasing fraction and determined that at or near 170 atmospheres the supersolid portion will disappear. "However, they have not carried the experiment to check this extrapolation because the sample cell exploded," says Chan.

A'ndrea Elyse Messer | EurekAlert!
Further information:
http://www.psu.edu

More articles from Physics and Astronomy:

nachricht MSU astronomers discovered supermassive black hole in an ultracompact dwarf galaxy
14.08.2018 | Lomonosov Moscow State University

nachricht ASU astrophysicist helps discover that ultrahot planets have starlike atmospheres
13.08.2018 | Arizona State University

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: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

Im Focus: World record: Fastest 3-D tomographic images at BESSY II

The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.

Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

'Building up' stretchable electronics to be as multipurpose as your smartphone

14.08.2018 | Information Technology

During HIV infection, antibody can block B cells from fighting pathogens

14.08.2018 | Life Sciences

First study on physical properties of giant cancer cells may inform new treatments

14.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>