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news release:
Strain Has Major Effect on High-Temp Superconductors
Gaithersburg, MD, 15 February 2007:
Just a little
mechanical strain can cause a large drop in the maximum current carried by
high-temperature superconductors, according to novel measurements carried out by
the National Institute of Standards and Technology (NIST).
The effect, which is reversible, adds a new dimension to designing
superconducting systems—particularly for electric power applications—and it also
provides a new tool that will help scientists probe the fundamental mechanism
behind why these materials carry current with no resistance.
The measurements, reported in
Applied Physics Letters,* revealed a 40 percent reduction in critical
current, the point at which superconductivity breaks down, at just 1 percent
compressive strain. This effect can be readily accommodated in the engineering
design of practical applications, NIST project leader Jack Ekin says, but
knowing about it ahead of time will be important to the success of many
large-scale devices. The effect was measured in three types of
yttrium-barium-copper-oxide (YBCO), a brittle ceramic considered the best
prospect for making low-cost, high-current, superconducting wires. The
researchers developed a “four point” bend technique that enables studies of
superconducting properties over a wide range of uniform strain at high current
levels. The superconductor is soldered on top of a flexible metal beam, which is
then bent up or down at both ends while the critical current is measured.
The discovery is the first major
reversible strain effect found in practical high-temperature superconductors,
which generally have been tested under smaller tensile strains only, or at
strains so high they caused the material to break down permanently. The newly
discovered effect is totally reversible and symmetric for both compressive and
tensile (pushing and pulling) strains, suggesting it is intrinsic to the
fundamental mechanism of superconductivity in YBCO.
The NIST team is now pursuing the
possibility of using the effect as a new tool for probing the elusive mechanism
underlying high-temperature superconductivity. The next step is to investigate
how magnetic fields affect the strain effect, and several collaborations are
under way with universities and other research organizations to study the
interplay of the effect with other factors affecting high-temperature
superconductivity. The research described in the new paper was supported in part
by the U.S. Department of Energy.
* D.C. van der Laan and J.W. Ekin. Large
intrinsic effect of axial strain on the critical current of high-temperature
superconductors for electric power applications. Applied Physics Letters,
90, 052506, 2006. Posted online Jan. 31
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