plastic gives electrons free ride
Technology Research News
note: this research has been withdrawn by the scientists.
Materials become superconducting when they lose all resistance to electricity,
allowing electrons to pass through them without losing energy to heat. This
is a potentially useful trait in electronics, because superconducting circuits
would use relatively little electricity and go very fast without heating
Although many metals are superconductors, the trait won't be practical for
use in common computer applications however, until researchers figure out
how to make substances superconducting in warmer temperatures or maintain
circuits at the extremely cold temperatures the phenomenon currently needs.
A group of scientists from Lucent Technologies' Bell Laboratories has added
a new material to the slate of known superconductors. The team has shown
that a plastic can be superconducting.
The researchers used a field effect transistor made of the organic polymer
film polythiophene, and caused it to superconduct electrons at temperatures
below 2.35 Kelvin, or -270.8 Celsius.
"Since polythiophene is an attractive material for electronics applications
and we [had] already fabricated polythiophene field effect transistors,
we were curious [about the possibilities of turning] this material from
insulating to superconducting," said Hendrick Schön, a scientist in Bell
Laboratories' condensed matter physics department. "At high densities in
low temperature we observed superconductivity," he said.
The researchers made the material superconducting when it was in a highly
ordered film, meaning it's individual molecules were neatly lined up. "We
found that the superconductivity can be suppressed by disorder in the film.
Therefore the structural organization of the material is very important,"
In contrast, metals are generally doped, or mixed with other materials,
to become superconducting. "The advantage [with plastic] is that only the
carrier concentration is varied,” and varying the concentration, or order
of a polymer is relatively easy to do, he said. "We used a very simple deposition
technique -- solution casting," said Schön.
This type of casting can be achieved at low temperatures without special
processing requirements like vacuums. It is also easy to put on flexible
substrates, he added.
The work is "impressive. [The researchers] have extended dramatically the
range of systems in which superconductivity is observed," said Dale J. VanHarlingen,
a physics professor at the University of Illinois at Urbana-Champaign. "This
is making all of us rethink what materials are likely to exhibit superconductivity."
It looks like the superconducting mechanism in polymers is different from
that of other known superconductors.
When metals superconduct, the electrons travel in a certain type of Cooper
pair. What's unusual about a Cooper pair is the electrons balance each other
with opposite and equal momentum. At low temperatures the Cooper pairs are
in a very low energy state, which allows them to accelerate together in
the presence of an electric field without scattering. Scattering is what
causes electrons to lose energy to heat in materials that are not superconductors.
In plastics, "it is likely that the symmetry and mechanism of the [electrons]
pairing will be different from that of the conventional... superconductors,"
said VanHarlingen, who added that the researcher's greatest challenge will
be "understanding how the microstructure of the films affects the superconducting
properties, and how to control it."
The advantage of plastic is it is easy to work with,VanHarlingen said. "A
lot is known about how to process and pattern polymer film into sophisticated
circuits. This implies that it may be possible to develop a superconducting
electronic technology based on polymers,” he said.
Along those lines, "the most exciting aspect [of plastic superconductors]
is the ability to tune the material from semiconducting to superconducting
by gating," said VanHarlingen. Gating, or applying current through the third
electrode of a field-effect transistor to control the current running through
the other two, has "long been studied in superconductors, but the effects
are not as striking as demonstrated here," he said.
The researchers are working to further tune the material's transition from
insulating to superconducting using an electrical current, said Schön.
Now that they have proved plastic can superconduct, the Bell researchers
are also working toward a goal many metallic superconductor researchers
have been working on for years -- making them superconduct at higher temperatures.
They are working to increase the transition temperature by making the polymers
even more ordered and by exploring the superconducting properties of different
kinds of organic polymers, said Schön.
It will probably be a long time before superconducting plastic can be used
in practical applications, said Schön. "I believe it will take much more
than two years to become practical. So far we are working on the lab scale
and trying to compare the first small superconducting circuits," he said.
The study of these materials, after all, is still in its infancy, said VanHarlingen.
"There's definitely potential for some interesting devices," he said, adding,
however that the low temperatures still required for superconductivity could
prohibit widespread practical uses.
Schön's research colleagues were Ananth Dodabalapur Zhenan Bao, space and
Christian Kloc, Of Bell Laboratories, Ortwin Schenker of the University
of Konstanz in Germany, and Bertram Batlogg of Bell Laboratories and the
Swiss Federal Institute of Technology (ETH). They published the research
in the March 8, 2001 issue of Nature. The research was funded by Lucent
Technologies and the University of Konstanz in Germany.
Timeline: > 2 years
Funding: Corporate, University
TRN Categories: Semiconductors and Materials
Story Type: News
Related Elements: Technical paper, "Gate-induced Superconductivity
into a Solution-processed Organic Polymer Film," Nature, March 8, 2001.
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