It may not be what Cary Grant had in mind when he uncovered
his elderly aunts' recipe for doing away with lonely bachelors in the
classic film, "Arsenic and Old Lace." But superconductors discovered a
few months ago by scientists in Japan are displaying remarkable
properties that present real mysteries to materials scientists.
The new class of materials that exhibit superconductivity at
relatively high temperatures contain no copper-oxygen layers. Instead
they have rather lace-like layers composed of arsenic and iron. A great
flurry of activity to understand these new superconductors is underway.
Researchers at the National High Magnetic Field Laboratory
(NHMFL), a facility established by the
National Science Foundation in
1990, are using high magnetic fields to probe the properties of these
materials, hoping to unlock the secret of their superconductivity.
Frank Hunte, a postdoctoral associate at the lab's Applied
Superconductivity Center (ASC), working with David Larbalestier, Alex
Gurevich, Jan Jaroszynski and colleagues in David Mandrus' group at Oak
Ridge National Laboratory in Tennessee, discovered surprising magnetic
properties in the new superconductors that suggest the materials may
have very powerful applications--from improved MRI machines and
research magnets to a new generation of superconducting electric
motors, generators and power transmission lines. The research, detailed
in the latest issue of the journal Nature, also adds to the long list
of mysteries surrounding superconductivity. The researchers present
evidence that the new materials, which scientists are calling "doped
rare earth iron oxyarsenides," develop superconductivity in quite a new
One of the most fascinating phenomena in nature,
superconductivity can be thought of as "frictionless" electricity. In
conventional electricity, heat is generated by friction as electrons
(electric charge carriers) collide with atoms and impurities in a wire.
This heating effect is good for appliances such as toasters or irons,
but not so good for most other applications that use electricity.
In some materials, a dramatic change takes place at very cold
temperatures--electric current glides through the materials without
dissipation. Powerful magnets that rely on this phenomenon of
superconductivity enable Magnetic Resonance Imaging for medicine, and
open new frontiers for scientific discovery at research centers such as
According to conventional wisdom, magnetic fields are to
superconductivity as Kryptonite is to Superman--progressively higher
magnetic fields weaken superconductivity until, at high enough magnetic
fields, superconductivity is gone. Researchers at the NHMFL use
powerful magnets to explore how the superconductivity in a new
superconducting material is weakened by magnetic fields. They are
finding that these new iron-arsenic materials are less susceptible to
the "Kryptonite" of magnetic fields than conventional wisdom would have
predicted. The discovery suggests that these iron-arsenic compounds
enable an entirely new kind of superconductivity.
Until the mid-1980s, all known superconductors exhibited
superconductivity at temperatures below a frigid -440 degrees
Fahrenheit (F), or about 2O degrees Kelvin. The discovery of the
so-called "high temperature superconductors" pushed the upper
temperature limit for superconductivity to a still frosty -200 degrees
F. The secret of how high-temperature superconductivity arises in these
materials revolves around electrons in layers composed of copper and
oxygen atoms. Unlike the "low temperature superconductors" which are
well described by the theory of superconductivity forged some 50 years
ago by (John) Bardeen, (Leon Neil) Cooper and (John Robert) Schrieffer
and polished into the standard theory of superconductivity by the work
of many others, the mechanism of superconductivity in the high
temperature superconductors remains a mystery.
In the mid-1980s, the first materials that exhibited
superconductivity at modest but comparatively high temperatures gave
way to the refined materials of today with much higher transition
temperatures. The discovery of the iron-arsenic materials, which
exhibit superconductivity at high temperature but do not contain the
signature copper-oxygen layers, could hold the key to understanding the
phenomenon of superconductivity at elevated temperatures more generally.
Though research on this substance is very much in its early
stages, scientists are talking excitedly of "promise" and "potential."
If scientists and engineers ever harness this phenomenon at or near
room temperature in a practical way, untold billions could be saved on
"What one would like is a greater selection of
superconductors, operating at higher temperatures, being cheaper,
possibly being more capable of being made into round wires," said
Larbalestier, director of the ASC. "Iron and arsenic, both inherently
cheap materials, are key constituents of this totally new class of
superconductors. We're just fascinated. It's superconductivity in
places you never thought of."