Proof of New State Of Matter is in the Jelly
In the community of very tiny particles that make up all matter in the
universe, there are two main citizens: bosons and fermions. Bosons are
socially oriented and tend to stick together, while fermions are
solitary entities, preferring to go it alone.
That’s why NASA-funded researchers overcame an important technical
challenge when they recently persuaded reclusive fermion atoms to act
like their friendly boson buddies and jiggle together in an
ultra-cold, jelly-like state of matter.
The findings, published in the online version of Physical Review
Letters, represent the first direct evidence for a fermion atom
superfluid – a frictionless fluid made up of a gas of fermion atoms.
Such bizarre atomic soups will help physicists understand how matter
behaves at its most fundamental level, and will serve as models for
exotic systems in nature, such as neutron stars and new super-
high-temperature superconductors that could potentially function at
thousands of degrees Celsius.
“When you build airplanes, you begin with small-scale models. The same
idea can be applied to very high-temperature superconductors, only the
models are fermionic superfluid gases,” said Dr. John Thomas, a
physics professor at Duke University, Durham, North Carolina, and
principal investigator for the new study. His research is funded by a
grant from NASA’s Office of Biological and Physical Research,
Washington, through the Jet Propulsion Laboratory, Pasadena, Calif.
Superconductors are materials that permit electrical currents to flow
without resistance. They have potential applications in the computer,
power and transportation industries. Rail system designers imagine
using superconductors to build magnetically levitated trains. But
current superconductors require impractically cold temperatures to
work. Fermionic superfluid gases – the atomic equivalent of
superconducting electrons – might serve as rudimentary blueprints for
creating superconductors that work at much higher temperatures.
The latest research builds on previous work by the Duke University
team outlining the creation of a possible fermion atom superfluid. In
that paper, reported in Science Magazine in 2002, the researchers used
an “optical bowl” made of a focused laser beam to trap lithium-6 atoms
(fermions) into a cigar-shaped cloud. They then chilled their
concoction to less than a millionth of a degree above absolute zero, a
temperature just above the point where no more cooling can occur, and
applied a small magnetic field.
The result was a transformation in character; the normally antisocial
atoms stacked up like peas in a pod and exhibited unusual behavior.
For instance, the gas expanded in one direction while standing still
in another when released from the bowl. Nonetheless, the researchers
could not find direct evidence that what they were seeing was an
actual superfluid – until now.
This time the researchers repeated the experiment at different
temperatures and then observed how long the fermionic gas jiggled, or
oscillated, after they switched the optical trap off and on,
essentially giving the gas a light tap. In a normal gas, collisions
between atoms should decrease as the temperature goes down, producing
an imperfect jelly whose oscillations die out quickly. In a
superfluid, the atoms act even more unified when temperatures are
lowered, and the oscillations should theoretically last forever. What
the team discovered was a jelly-like gas that wobbled for increasingly
longer times as the temperature decreased – the first direct signs of
a fermion atom superfluid and the beginnings of a new model for
exploring the possibility of extremely high-temperature
superconductors.
Other authors include Duke University researchers Joe Kinast, Staci
Hemmer, Mike Gehm and Andrey Turlapov. More information on the
research is available at:
http://www.dukenews.duke.edu/news/superfluid_0404.html. The press
release about the previous Duke University fermion research is at:
http://www.jpl.nasa.gov/releases/2002/226.cfm.
