Johns Hopkins University researchers and colleagues in
China have unlocked some of the
secrets of newly discovered iron-based high-temperature
superconductors, research that could result
in the design of better superconductors for use in
industry, medicine, transportation and energy
generation.
In an article published June 4 in the journal Nature,
the researchers, led by Chia-Ling Chien,
the Jacob L. Hain Professor of Physics and director of
the
Materials Research Science and
Engineering Center at Johns Hopkins, offer insights
into why the characteristics of a new family of
iron-based superconductors reveal the need for fresh
theoretical models that could, they say, pave
the way for the development of superconductors that can
operate at room temperature.
"It appears to us that the new iron-based
superconductors disclose a new physics, contain new
mysteries and may start us along an uncharted pathway to
room temperature superconductivity," said
Chien, who teamed up on the research with Tingyong Chen and
Zlatko Tesanovic, both of Johns
Hopkins, and X.H. Chen and R.H. Liu, both of the Hefei
National Laboratory for Physical Sciences at
Microscale and the Department of Physics, University of
Science and Technology of China, in Anhui,
China.
Superconductors are materials that can carry
electrical current without friction and, as a
result, don't waste electrical energy generating heat.
(Imagine your laptop computer or PC not getting
warm when it is turned on.) This means that an electrical
current can flow in a loop of superconducting
wire forever without a power source. Today, superconductors
are used in hospital MRI machines, as
filters in cell phone base stations and in high-speed
magnetic levitation trains.
Most of today's superconducting materials can function
and operate only at extremely low
temperatures, which means that they must be paired with
expensive supercooling equipment. This
presents researchers with a grand challenge: to find
superconducting material that can operate at
more "normal" temperatures.
"If superconductors could exist at room temperatures,
the world energy crisis would be solved,"
Chen said.
Though all metals contain mobile electrons that
conduct electricity, a metal becomes a
superconductor only when two electrons with opposite
"spins" are paired, Chen said. The
superconductor energy "gap," which is the amount of energy
that would be needed to break the bond
between two electrons forming such a pair to release them
from one another, determines the
robustness or strength of the superconducting state. This
energy gap is highest at low temperatures
but vanishes at the temperatures at which superconductivity
ceases to exist.
"This gap — its structure and temperature
dependence — reveals the 'soul' of the
superconductor,
and this is what was measured in our experiment," Chien
said.
The team measured this gap and its temperature
variation, revealing that the pairing mechanism
in iron-based superconductors is different from the one in
more traditional copper-based, high-
temperature superconductors. To the researchers' surprise,
their results were incompatible with some
of the newly proposed theories in this mushrooming
field.
"In the face of this discovery, it is clear that we
need to re-examine the old and invent some
new theoretical models," Tesanovic said. "I predict that
these new, iron-based superconductors will
keep us physicists busy for a long, long while."
This research was supported by the U.S. National
Science Foundation and the Natural Science
Foundation of China.