Iron in the mix
Scientists look for the secret behind
high-temperature superconductors
By Gwyneth Dickey
Only copper-oxide superconductors
work at higher temperatures than the
iron-based family, and together the two
groups make up what are known as the
high-temperature superconductors.
Scientists have been trying to figure
out how high-temperature supercon-
ductivity works since copper oxides, or
cuprates, were found to exhibit resis-
tance-free flow in 1986. Right now, even
the most promising
cuprate must be cooled
to about 138 kelvins.
Though liquid nitrogen
can get materials that
cold fairly easily, the
cuprates are hard to
form into wires.
Physicist Johnpierre Paglione works in a kitchen of sorts: He precisely blends ingredients, heats his mixtures to just the
right temperature and cools them to
get the perfect product. But rather than
only edible ingredients, his recipes call
for toxic chemicals, such as arsenic,
and metals — especially
iron. His ovens, which
line the shelves of his
lab at the University
of Maryland in College
Park, reach 1,700˚ Celsius before he carefully
cools his concoctions
over days or weeks.
When the timer finally
dings, out pops a sil-very-black pebble with
one flat, shiny surface.
Thousands of papers have been
The newly made pebble is a super-
conductor, a material that shuttles
electricity with essentially perfect effi-
ciency, defying the resistance that typi-
cally slows electrons down. Because
Paglione’s pebble incorporates iron
into its molecular structure, it’s a mem-
ber of a new class of materials known
as iron-based superconductors. These
materials, discovered in 2008, work at
temperatures as high as −218˚ Celsius, or
55 kelvins (degrees above absolute zero).
Though that sounds pretty cold, conven-
tional superconductors must be cooled
to within a few degrees of absolute zero.
With the new iron
family on the scene,
“The field is feeling very liberated
and very excited and very optimistic,
because we’re not constrained to ‘it’s just
copper oxide, it’s just iron arsenide,’”
says physicist Paul Canfield of Iowa
State University in Ames and the U.S.
Department of Energy’s Ames Laboratory. “It may be that if we can figure out
what’s similar between these two very
different classes of materials, we may be
able to generalize and find other materials that may even have more promising
properties.”
Iron-based superconductors are built
with layers. The one shown includes iron
(red), arsenic (purple) and barium (blue).
