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Researchers peg magnetism as key
driver of high-temperature superconductivity
Gaithersburg, MD, July 6: When it comes to
superconductivity, magnetic excitations may top good vibrations.
Writing in the July 6, 2006, issue of Nature,
scientists working at the Commerce Department's National Institute of Standards
and Technology (NIST) Center
for Neutron Research (NCNR)
in collaboration with physicists from the University of Tennessee (UT)
and Oak Ridge National Laboratory (ORNL)
report strong evidence that magnetic fluctuations are key to a universal
mechanism for pairing electrons and enabling resistance-free passage of electric
current in high-temperature superconductors.
An important missing piece in the puzzle of
high-temperature superconductivity, the finding should boost efforts to develop
a variety of useful technologies now considered impractical for conventional
superconductors, which work at markedly lower temperatures. Examples include
loss-free systems for storing and distributing electric energy, superconducting
digital routers for high-speed communications, and more efficient generators and
motors.
The team was led by Pengcheng Dai, a UT-ORNL
joint professor.
"Our results unify understanding of the role of
magnetism in high-temperature superconductivity and move the research community
one step closer to understanding the underlying pairing mechanism itself," says
NIST physicist Jeffrey Lynn, a member of the collaboration. Better understanding
of the mechanism of high-temperature superconductivity may lead to the discovery
of new materials in which electrical resistance vanishes at even warmer
temperatures.
Objects of intense scientific and technological
interest since their discovery in 1986, high-temperature superconductors work
their magic in ways different than materials that become superconducting at
significantly colder temperatures, as first observed in 1911. In these
conventional superconductors, vibrations in the materials' atomic latticework
mediate the pairing process that results in the unimpeded flow of electrons.
Scientists have ruled out vibrations, or phonons,
as the likely electron matchmaker in high-temperature superconducting compounds.
And while they have assembled important clues over the last two decades,
researchers have yet to pin down the electron-pairing mechanism in the
high-temperature superconductors.
"Various experiments and theories have suggested
that this resonance--this sharp magnetic excitation--may be the glue needed to
explain high-temperature superconductivity, but key pieces of evidence were
missing," explains lead author Stephen Wilson, a UT graduate student.
Previous work by other researchers had determined
that magnetism played a role in one of two major classes of high-temperature
superconductors--those engineered with holes, or occasional vacancies where
electrons normally would reside. But, until this work, carried out at NCNR and
ORNL's High Flux Isotope Reactor, the underlying pairing mechanism in the other
class--materials doped with an excess of electrons--eluded detection.
Using neutron probes, which are extremely
sensitive to magnetism, the team was the first to observe a magnetic resonance
in an electron-doped high-temperature superconductor, in a carefully engineered
compound known as PLCCO. More importantly, the resonance energy was found to
obey a well-established relationship universal to high-temperature
superconductors, irrespective of type.
This demonstrated a fundamental link between
magnetism and the superconducting phase, the researchers report. These
observations and findings should open new avenues of research into the exotic
properties of high-temperature superconductors, they write.
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