Discovery - Quantum Oscillations in Superconductors
Posted on Sunday, June 03, 2007 @ 11:08:35 UTC by vlad
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Physicist Louis Taillefer's excitement for making an internationally
important scientific discovery from Sherbrooke is comparable to that of
a kid on Christmas morning.
But instead of finding presents under the tree, Taillefer's excitement
comes from finding "quantum oscillations" in superconductors.
"It's going to transform our lives. It's going to cause a major
technological transformation," he said, his eyes widening at the
possibilities. It's the most important discovery of his career.
To understand where this is headed, it's essential to understand where it all began.
Superconductors can conduct electricity without any resistance,
so no energy is ever lost. The problem is these materials only function
at unimaginably low temperatures.
Two decades ago, materials were discovered that could super
conduct at much higher temperatures: minus-109 degrees Celsius. "This
is probably not room temperature anywhere on Earth, but from our
perspective, it's not that far from room temperature," Taillefer said.
"Twenty years now since this discovery, and we are still
basically in the clouds. We are still in thick fog as to why these
materials behave like they do."
That is, until yesterday, when University of Sherbrooke researcher Taillefer announced the discovery of quantum
oscillations.
"These oscillations are literally wiggles in the resistance -
they are the voice of the electrons in the most pristine, direct way."
In other words, it is now possible to know how superconductors operate at the microscopic level.
"We now have a clear track to follow to develop a complete understanding of the materials," Taillefer said.
While this discovery isn't the final step in understanding the
full potential of superconductors, it tells scientists where to focus.
"Within a year, we will basically know what the electrons are doing,"
he said. Researchers will be well on their way to solving one of the
most important scientific questions of the day: how to make a
superconductor work at room temperature.
"We are going to have a better idea of which knobs to turn,
how to tweak the structure to move the critical temperature up,"
Taillefer said.
"Reaching room temperature superconductivity for many is the holy grail."
But Taillefer is the first to admit that this may not sound as
exciting for average citizens, who simply wants to know how their lives
will change for the better.
That question is hard to answer.
He compares it to the invention of transistors in the 1940s.
"Look around you right now. We have Google today, because we have
transistors," he said. "In the same way you never could have predicted
Google from a transistor when it first arrived, you cannot predict what
having a room-temperature superconductor will do in the long term."
Today, superconductors are used most commonly in magnetic
resonance imaging, more commonly known as MRIs. It could be that "MRIs
would shrink from the size of a garden shed to the size of a laptop,"
he said.
The mere possibilities of where this technology could lead is
causing researchers to jump on board. "Now there's a tidal wave. We are
trying to stay ahead of it. But we are a small boat, here in
Sherbrooke."
The discovery came from Taillefer and his team of three
students: a post-grad, Nicolas Doiron-Leyraud, Ph.D. student David
LaBoeuf and Masters student Jean-Baptiste Bonnemaison.
While Taillefer takes pride in his accomplishment, he also takes pleasure in relating how his team got there.
"I am fascinated by the origin of discovery. Why some people
make discoveries, and why others don't," he said. "And I can tell you
why we succeeded and others failed."
He said three essential ingredients separated his team from all others.
"We had the best crystals in the world," Taillefer said,
explaining that observing the oscillations was directly based on the
quality of the oxide crystals used. (Taillefer and his team have been
collaborating with the University of British Columbia, which has been
perfecting these crystals for 20 years.)
The second necessary ingredient is a huge magnetic field. "You
need a magnetic field of the order of a million times the Earth's
magnetic field."
There is no lab with this capability in Canada, so Taillefer and his team had to travel.
Those two technical aspects were mixed with a third ingredient: intuition.
Taillefer and his team had a hunch about a specific oxygen
concentration in the superconductor, and they focused all their
attention on this one spot. "We persisted in that direction, while
others went away to look somewhere else."
There was one more thing: an accident.
"The guys broke off a wire, and they had only one wire left,"
Taillefer said. They had been using two wires parallel to each other,
but with only one wire left, "they did a diagonal contact, and they saw
the oscillations."
And so on "the 27th of February, my three students called me
[from France] and said 'Louis, look at your screen'. And I saw these
beautiful oscillations. That was a real eureka moment!"
His enthusiasm is shared by the rest of the science community.
Yesterday Taillefer and his team published their findings in Nature -
one of the most prestigious magazines in science. The article was
accepted in a record 15 days.
Taillefer said, "I suggested that the title of the article should be 'Hottest Science Paper of the Year!'"
A less original title was chosen, but Taillefer said the importance of this article will not be lost.
"This stuff is very, very hot."
June 1
By Christopher Doody
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Little-Parks effect
- Little-Parks oscillation provides a direct proof of the quantum
behavior of electrons in a superconductor. In their experiments (1962),
William A. Little and Roland D. Parks demonstrated that the electrons,
which form a quantum-coherent condensate in superconducting metals,
such as tin or lead, exhibit a sensitivity to the vector-potential, and
not only to the magnetic field as non-quantum charged particles.
Little-Parks oscillation occurs in hollow superconducting cylinders,
pierced by a magnetic field. The critical temperature and thus the
electrical resistance oscillate periodically as the magnetic field is
gradually increased. The period is defined as the superconducting
magnetic flux quantum h/2e divided by the area of the cross-section of
the cylinder. Thus one period of oscillation corresponds to an increase
of the magnetic flux through the cylinder by one flux quantum h/2e.
Based on quantum theory one expects that the LP oscillation of the
critical temperature should occur even if the magnetic field is
completely confined inside the cylinder, without entering into the
superconducting walls of the cylinder. This prediction has never been
tested experimentally.
Via: http://www.keelynet.com/#whatsnew
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