The 'new age' of super materials
By Jonathan Fildes Science and technology reporter, BBC News
In 1987, Ronald Reagan declared that the US was about to enter an
incredible new era of technology.
Levitating high-speed trains, super-efficient power generators and
ultra-powerful supercomputers would become commonplace thanks to a
new breed of materials known as high temperature superconductors
(HTSC).
"The breakthroughs in superconductivity bring us to the threshold of
a new age," said the president. "It's our task to herald in that new
age with a rush."
But 20 years on, the new world does not seem to have arrived. So what
happened?
Early promise
Superconductivity was first discovered in 1911 by researchers at the
University of Leiden who used solid mercury in their experiments.
Superconductors have no electrical resistance, so unlike conventional
conductors they allow an electric current to flow through without any
loss.
At the start, the phenomenon was only seen in materials cooled close
to absolute zero, which according to theory is the state of zero heat
energy.
Three-quarters of a century later, the highest temperature achieved
for the onset of superconductivity, the so-called transition
temperature, was a frigid 23 Kelvin (-250C).
This allowed scientists to exploit the phenomenon in specialist
applications such as Magnetic Resonance Imaging (MRI) scanners and
high energy physics particle colliders, cooled by liquid helium.
But more day-to-day applications, such as replacing the electricity
grid with superconducting wires, remained impossible without
materials able to operate at higher temperatures.
Closer to zero
The breakthrough came in 1986.
Two IBM researchers, Georg Bednorz and Alex Mueller, discovered a new
family of ceramic superconductors, known as the copper oxide
perovskites, that operated at 35K (-238C)
The work was rapidly followed up Paul Chu, of the University of
Houston, who discovered materials operating at 93K (-182C)
The discovery meant that superconductors had entered the temperature
range of liquid nitrogen (77K, -196C), an abundant and well
understood coolant.
"All of a sudden everything was different," said Professor Chu.
"There was a euphoric feeling. People in the field thought nothing
was impossible."
The discovery prompted a huge gathering of physicists in New York to
discuss the breakthrough, a meeting later called the "Woodstock of
Physics".
Precise structure
But large-scale commercialisation of the technology would prove more
difficult.
"The material was not as simple as we originally thought," said
Professor Chu.
Despite an intensive two-decade search, the underlying mechanism of
superconductivity in the ceramics is still disputed.
In addition, their exact structure, requiring ultra-thin layers of
different elements stacked on top of each other, means they are very
difficult and expensive to manufacture.
"Atomically, you have to line them up very precisely in order for the
supercurrent to flow," explained Professor Chu.
This, coupled with the fact that ceramics are brittle and difficult
to turn into flexible wires and films, meant that prospects for
immediate exploitation were not good.
"I think the expectations were a little unrealistic," said Dr Dennis
Newns of IBM.
"The typical time it takes from inventing a new concept to
application is 20 years," he said. "And that is exactly what we have
seen."
Cool running
Companies in Japan, Europe, China, South Korea and the US are forging
ahead with applications.
In the US, American Superconductor has developed a way to "bend the
unbendable", creating HTSC wires that can carry 150 times more
electricity than the equivalent copper cables.
"Twenty years ago you would see people making ceramic fibres and
trying to bend them and it was like a dry stick of spaghetti," said
Greg Yurek, CEO and founder of the company.
To get around this brittleness, the company embeds up to 85 tiny
filaments of superconducting ceramic in a ribbon of metal 4.4mm (0.17
inches) wide.
"Think of optical fibres," said Dr Yurek. "If you have a rod of glass
and you whack it on your desk it will shatter.
"Drop down to a fine optical fibre and it becomes flexible - it's the
same principle here."
The company also produces wires with a coating of the ceramic just
one micron (millionth of a metre) thick on a metal alloy. Both are
cooled by a sheath of liquid nitrogen.
Short sections of the wires have already been installed in Columbus,
Ohio, and a further half-mile of cable will soon be laid on Long
Island, New York.
In the short term, longer stretches of the supercooled cable will be
difficult to install, as it requires an infrastructure to pump liquid
nitrogen around the grid.
But Dr Yurek believes that it will not be long before other firms
start to offer utility companies these cryogenic services.
"This is the model they have used in the MRI industry to guarantee
the cold," he said.
Shrinking motors
The company also promotes its HTSC wires for other advanced
applications.
Central Japan Railways uses coils of it for their superconducting
experimental magnetic levitation (maglev) train.
American Superconductor has also developed an electric motor using
coils of superconducting wire for use in the next generation of US
Navy destroyers.
Electric motors are used by most commercial cruise liners, but are
typically very bulky.
Using HTSC technology dramatically shrinks their size and also
increases their efficiency.
The company is just about to start testing its latest 36.5-megawatt
engine that is cooled by off-the-shelf liquid helium refrigerators
and weighs 75 tonnes. By comparison, an engine based on copper wires
would weigh 300 tonnes.
"That's great for cruise ships and the navy, because they can use
that space for other things like passenger cabins or munitions," said
Dr Yurek.
"New age"
Experimentally, things have also moved on.
New superconductors have been found. For example, a new mercury-based
compound has a transition temperature of 134K (-139C)
"When we applied pressure we raised it up to 164K (-109C) - that's a
record," said Professor Chu.
"Of course from an application point of view, it's hopeless."
However, other experimental work raises the possibility of
discovering room temperature superconductors that would require no
exotic cooling equipment.
A new theory, outlined in a paper in the journal Nature Physics by Dr
Newns and his IBM colleague Dr Chang Tsuei, seeks to explain the
elusive mechanism of superconductivity in the class of ceramics
discovered in 1986.
"We don't see any fundamental limits," said Dr Tsuei.
"If someone discovered a room-temperature superconductor tomorrow
that fits with what is outlined by our theory, we wouldn't be
surprised at all," added Dr Newns.
This kind of optimism, seen for the first time in the mid-1980s, now
seems to be deserved.
There has been a crescendo of research, while at the same time the
first commercial HTSC products are rolling out of factories.
According to Dr Yurek, this is a sign that the new age promised by
Ronald Reagan is finally here.
"I think we're on a launching pad here and we're now ready to take
off," he said.
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