Superinsulation may sound like a marketing gimmick for a
drafty attic or winter coat. But it is actually a newly-discovered
fundamental state of matter created by scientists at the U.S.
Department of Energy's (DOE) Argonne National Laboratory in
collaboration with several European institutions. This discovery both
opens new directions of inquiry in condensed matter physics and breaks
ground for a new generation of microelectronics.
Led by Argonne senior scientist Valerii Vinokur and Russian
scientist Tatyana Baturina, an international team of scientists from
Argonne, Germany, Russia and Belgium fashioned a thin film of titanium
nitride with they then chilled to near absolute zero. When they tried
to pass a current through the material, the researchers noticed that
its resistance suddenly increased by a factor of 100,000 once the
temperature dropped below a certain threshold. The same sudden change
also occurred when the researchers decreased the external magnetic
field.
"Titanium nitride films as well as films prepared from some
other materials can be either superconductors or insulators depending
on the thickness of the film. If you take the film which is just on the
insulating side of the transition and decrease the temperature or
magnetic field, then the film all of a sudden becomes a
superinsulator," Vinokur said.
Like superconductors, which have applications in many
different areas of physics, from accelerators to magnetic levitation
(maglev) trains to MRI machines, superinsulators could eventually find
their way into a number of products, including circuits, sensors and
battery shields.
If, for example, a battery is left exposed to the air, the
charge will eventually drain from it in a matter of days or weeks
because the air is not a perfect insulator, according to Vinokur. "If
you pass a current through a superconductor, then it will carry the
current forever; conversely, if you have a superinsulator, then it will
hold a charge forever," he said.
Additionally, scientists could eventually form superinsulators
that would encapsulate superconducting wires, creating an optimally
efficient electrical pathway with almost no energy lost as heat. A
miniature version of these superinsulated superconducting wires could
find their way into more efficient electrical circuits.
Titanium nitride's sudden transition to a superinsulator
occurs because the electrons in the material join together in twosomes
called Cooper pairs. When these Cooper pairs of electrons join together
in long chains, they enable the unrestricted motion of electrons and
the easy flow of current, creating a superconductor. In
superinsulators, however, the Cooper pairs stay separate from each
other, forming self-locking roadblocks. "In superinsulators, Cooper
pairs avoid each other, creating enormous electric forces that oppose
penetration of the current into the material,” Vinokur said.
"It's exactly the opposite of the superconductor," he added.
The theory behind the experiment stemmed from Argonne's
Materials Theory Institute, which Vinokur organized six years ago in
the laboratory's Materials Science Division. The MTI hosts a handful of
visiting scholars from around the world who then perform cutting-edge
research on the most pressing questions in condensed matter physics.
Upon completion of their tenure at Argonne, these scientists return to
their home institutions but continue to collaborate on the joint
projects. The MTI attracts the world's best condensed matter
scientists, including Russian "experimental star" Tatyana Baturina,
who, according to Vinokur, "became a driving force in our work on
superinsulators."
Posted 9th April 2008
