New research sheds light on shimmering superconductivity and the courtship
of electrons
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Argonne, Ill. (Oct. 3, 2007) – In their normal state, electrons repel each
other because of their charge, but in the state of superconductivity, electrons
pair up. John Schlueter, a chemist from the U.S. Department of Energy's Argonne
National Laboratory, collaborated with a team of researchers from the University
of Oxford to better understand how this unlikely courtship occurs.
Their recent
research appears in the October 4 issue of Nature and finds that a form of
shimmering superconductivity exists at temperatures well above that at which
ordinary superconductivity is destroyed. This electron courtship is characterized
by a tension between the conflicting urges for electrons to pair up (which
leads to superconductivity) and to repel each other (which leads to insulating
behavior).
Superconductors conduct electricity with absolutely no resistance when cooled
below a certain critical temperature, Tc. “Superconductivity already
has important applications and many more uses are possible if critical temperatures
are high enough,” Schlueter explained.
Much research over the past decade has focused on inorganic cuprate superconductors.
Although molecular superconductors currently have maximum Tcs near
10 K (nearly an order of magnitude lower than the cuprates), they have many
features that make them ideal for the study of the fundamental properties of
superconductivity. In the organic materials, lower temperatures and magnetic
fields are required to reach the boundaries between superconducting and normal
states, thus making these experiments much easer to perform in a laboratory.
Although such shimmering superconductivity above the usual temperature barrier
has previously been observed in cuprate materials, this is the first time it
has been seen in an extremely clean and well controlled system that doesn't
have to be chemically doped to produce superconductivity. This means that scientists
can be sure that the effect is not associated with impurities. In fact, the
team believes that such an effect should be found in all superconductors in
which conflicting interactions are finely balanced. This is an important step
forward in the quest to understand superconductivity in what are known as "highly
correlated" materials: the superconductors of the future.
The Argonne group has long been recognized as an international leader in the
discovery and crystallization of high quality crystals of molecular superconductors. “We
use an electrocrystallization technique both as a discovery tool and a means
to enable sophisticated measurements aimed at unraveling some of the outstanding
mysteries of superconductivity,” Schlueter explained. This research was performed
on a superconducting material discovered by the Argonne group in 1990, addresses
a longstanding question relating to the pairing of electrons in superconducting
materials. The study identifies similarities between the high and low temperature
superconductors.
The discovery was made by Moon-Sun Nam in collaboration with Arzhang Ardavan
and Stephen Blundell in Oxford University's Department of Physics, using crystals
grown by John Schlueter. The team exploited a particularly sensitive probe
of superconducting fluctuations called the "vortex-Nernst effect".
This effect provides a way of detecting that superconducting vortices are present,
even when zero electrical resistance (the characteristic of traditional superconductivity)
is not exhibited.
The funding for this research was provided by the Department of Energy's Office
of Basic
Energy Sciences, Division of Material
Sciences and Engineering.
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For more information, please
contact Steve McGregor (630/252-5580 or media@anl.gov)
at Argonne.
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