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Physicists reveal superconducting surprise
Posted on Wednesday, February 13, 2008 @ 22:50:04 UTC by vlad
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 MIT physicists have taken a step toward understanding the puzzling
nature of high-temperature superconductors, materials that conduct
electricity with no resistance at temperatures well above absolute zero.
If superconductors could be
made to work at temperatures as high as room temperature, they could
have potentially limitless applications. But first, scientists need to
learn much more about how such materials work.
Using a new method, the MIT
team made a surprising discovery that may overturn theories about the
state of matter in which superconducting materials exist just before
they start to superconduct. The findings are reported in the February
issue of Nature Physics.
Understanding high-temperature superconductors is one of the
biggest challenges in physics today, according to Eric Hudson, MIT
assistant professor of physics and senior author of the paper.
Most superconductors only superconduct at temperatures near
absolute zero, but about 20 years ago, it was discovered that some
ceramics can superconduct at higher temperatures (but usually still
below 100 Kelvin, or -173 Celsius).
Such high-temperature superconductors are now beginning to be used
for many applications, including cell-phone base stations and a demo
magnetic-levitation train. But their potential applications could be
much broader.
"If you could make superconductors work at room temperature, then the applications are endless," said Hudson.
Superconductors are superior to ordinary metal conductors such as
copper because current doesn't lose energy as wasteful heat as it flows
through them, thus allowing larger current densities. Once a current is
set in motion in a closed loop of superconducting material, it will
flow forever.
In the Nature Physics study, the MIT researchers looked at a state
of matter that superconductors inhabit just above the temperature at
which they start to superconduct.
When a material is in a superconducting state, all electrons are at
the same energy level. The range of surrounding, unavailable electron
energy levels is called the superconducting gap. It is a critical
component of superconduction, because it prevents electrons from
scattering, thus eliminating resistance and allowing the unimpeded flow
of current.
Just above the transition temperature when a material starts to
superconduct, it exists in a state called the pseudogap. This state of
matter is not at all well understood, said Hudson.
The researchers decided to investigate the nature of the pseudogap
state by studying the properties of electron states that were believed
to be defined by the characteristics of superconductors: the states
surrounding impurities in the material.
It had already been shown that natural impurities in a
superconducting material, such as a missing or replaced atom, allow
electrons to reach energy levels that are normally within the
superconducting gap, so they can scatter. This can be observed using
scanning tunneling microscopy (STM).
The new MIT study shows that scattering by impurities occurs when a
material is in the pseudogap state as well as the superconducting
state. That finding challenges the theory that the pseudogap is only a
precursor state to the superconductive state, and offers evidence that
the two states may coexist.
This method of comparing the pseudogap and superconducting state
using STM could help physicists understand why certain materials are
able to superconduct at such relatively high temperatures, said Hudson.
"Trying to understand what the pseudogap state is is a major outstanding question," he said.
Lead author of the paper is Kamalesh Chatterjee, a graduate student
in physics. MIT physics graduate students Michael Boyer and William
Wise are also authors of the paper, along with Takeshi Kondo of the
Ames Laboratory at Iowa State University and T. Takeuchi and H. Ikuta
of Nagoya University, Japan.
Source: MIT, by Anne Trafton
Via: http://www.physorg.com/news122048727.html
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SUPERCONDUCTING CHAOS (Score: 1)
by vlad on Wednesday, February 13, 2008 @ 23:13:14 UTC
(User Info | Send a Message) http://www.zpenergy.com | A new experiment at Colorado State University studies the chaotic dynamics of *flux drops*-microscopic swirling eddies of supercurrent-that flow along a narrow channel crossing a superconducting strip. An applied current perpendicular to the channel causes a flux drop to nucleate, grow, and break off at the end of the channel. The drop is then driven along the channel by the current. This process is reminiscent of water drops dripping from a nozzle, for a long time of the chief methods for understanding chaos. The Colorado State investigators used a micron-sized magnetic sensor to directly detect the magnetic field of individual drops as they passed beneath it. The resulting time sequence of flux drops, just like that of water drops from a faucet, exhibits clear signatures of deterministic chaos, implying that the irregular-looking sequence of drops is not random, but predictable from knowledge of earlier drop times. However, predicting the sequence more than 4 or 5 drops into the future becomes exponentially difficult-another hallmark of chaos. According to Stuart Field (field@lamar.colostate.edu, 970-491-3773) this is the first conclusive observation of chaotic behavior in moving flux structures. The direct observation of the time series allows for an unambiguous identification of chaos in this system. (Field and Stan, Physical Review Letters, upcoming article; designated as an Editor*s suggested article)
From: PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 856 February 13, 2008 www.aip.org/pnu
by Phillip F. Schewe and Jason S. Bardi
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