
RESEARCHERS PEG MAGNETISM AS KEY DRIVER OF HIGH-TEMPERATURE SUPERCONDUCTIVITY
Date: Thursday, July 06, 2006 @ 22:57:38 UTC Topic: Science
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 Center
for Neutron Research in collaboration with physicists from the University of
Tennessee and Oak Ridge National Laboratory 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.
Source: National Institute of Standards and Technology
Link: http://www.physorg.com/news71327771.html -----------
NANO WORLD: NANOMAGNETS IN CHIPS, ANTENNA, July 05 Magnetic particles only
nanometers or billionths of a meter wide promise to help electronics continue to
pack ever closer together for more powerful microchips and other devices,
experts told UPI's Nano World. Full story at http://www.physorg.com/news71336966.html
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