Re: New Iron Age for Physics?
- From: "RichL" <rpleavitt@xxxxxxxxx>
- Date: Thu, 29 May 2008 12:17:47 GMT
Mackenzie <jade_f45@xxxxxxxxx> wrote:
This is an article based on the findings of a high-temperature
superconductor based on iron that I found in the breakroom at the
office. Someone had it and I read it with interest. This is quite the
discovery for physicists:
For more than 20 years, the only known superconductors that worked far
above liquid-helium temperatures were a few dozen compounds- virtually
all based on copper. Now scientists have discovereed the first high-
temperature superconductors based on iron. These novel materials could
help unravel one of the biggest mysteries in science- how exactly the
high temperature versions work.
In superconductors electric current flows completely without
resistance. For decades, the phenomenon was thought to occur only near
absolute zero. The cold tames the vibrations of the atoms making up
the substance in such a way that electrons can overcome their natural
repulsion for one another. The altered vibrations, called phonons,
cause the electrons to pair up; so coupled, they can then move freely
through the atomic lattice.
Starting in 1986, however, physicists began discovering a new class of
superconductors operating well above absolute zero, to temperatures as
high as 160 kelvins. These materials, dubbed cooperates, typically
consist of copper oxide layers sandwiched between other substances.
The structure of the cuprates and the high temperature interfere with
the mechanisms that drive conventional superconductors, leading
physicists to try to come up with new explanations.
A serendipitous discovery is now forcing investigators to expand their
ideas on superconductivity. Materials scientist Hideo Hosono of the
Tokyo Institute of Technology and his colleagues were looking to
improve the performance of transparent oxide semiconductors but ended
up discovering the first iron-based, high temperature superconductor.
The crystalline material, known chemically as LaOFeAs, stacks iron and
arsenic layers, where the electrons flow, between planes of lanthanum
and oxygen. Replacing up to 11 percent of the oxygen with fluorine
improved the compound- it became superconductive at 26 kelvins, the
team reports in the March 19 Journal of the American Chemical Society.
Subsequent research from other groups suggests that replacing the
lanthanum in LaoFeAs with other rare earth elements such as cerium,
samarium, neodymium and praseodymium leads to superconductors that
work at 52 kelvins.
High-temperature superconductivity in these layered iron compounds
completely surprised investigators, who thought that the magnetic
nature of iron would disrupt the pairing of electrons. Perhaps, as
seems to be the case for cuprates, the electrons get paired with the
aid of spin fluctuations- disturbances in the magnetic fields of atoms
making up the superconductor.
?These iron-based superconductors could give us new hints on how to
understand cuprates,? says physicist Kristjan Haule of Rutgers
University.
On the other hand, the spin fluctuations that could glue together
cuprate electrons might not be enough for those in the iron-based
materials. Instead orbital fluctuations- or variations in the location
of electrons around atoms- might also prove crucial, Haule
speculates.
In essence, the iron-based materials give more freedom to electrons
than cuprates do when it comes to how electrons circle around atoms.
Orbital fluctuations might play important roles in other
unconventional superconductors as well, such as ones based on uranium
or cobalt, which operate closer to absolute zero, Haule conjectures.
Because the iron-based superconductors work at higher temperatures,
such fluctuations may be easier to research.
Besides illumination the theoretical underpinnings of
superconductivity, the discovery ?makes us ask if there are other
high- temperatures superconductors we haven?t found yet in unexpected
places and if there are even higher temperatures these can work at,?
remarks theoretical physicist David Pines of the University of
California, Davis, who is also founding director of the Institute for
Complex Adaptive Matter. In trying to boost the critical temperature,
experiments should focus not only on swapping in other elements but
also on layering the compounds. That should improve them just as it
does for cuprate superconductors, Haule thinks.
Being based on iron could make these substances more commercially
enticing too. The fragility of cuprates, which as ceramics are quite
brittle has long hampered applications such as superconductoring
lines. If iron-based materials are easier to handle than cuprates,
?they will become very important
Cool stuff (literally!).
Source:
http://www.sciam.com/article.cfm?id=iron-exposed-as-high-temp-superconductor
.
- Follow-Ups:
- Re: New Iron Age for Physics?
- From: Mackenzie
- Re: New Iron Age for Physics?
- References:
- New Iron Age for Physics?
- From: Mackenzie
- New Iron Age for Physics?
- Prev by Date: Re: Bush war.....
- Next by Date: Re: Bush war.....
- Previous by thread: Re: New Iron Age for Physics?
- Next by thread: Re: New Iron Age for Physics?
- Index(es):
Relevant Pages
|
