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'Stripes' And Superconductivity: Two Faces Of The Same Coin?
Science Daily ^ | 12-5-2006 | Cornell University

Posted on 12/05/2006 4:04:12 PM PST by blam

'Stripes' And Superconductivity: Two Faces Of The Same Coin?

Researchers at Brookhaven National Laboratory and Cornell have made a surprising discovery about the behavior of high-temperature superconductors that could be a further step toward understanding how these valuable materials work.

Scanning tunneling microscope photo of the surface of a sample of non-superconducting material. Whether or not the lined pattern seen here corresponds to the "striped" arrangement of electron pairs in the material is still to be determined, according to Cornell physicist J.C. Séamus Davis. (Image courtesy of Cornell University)

Previous experiments have shown that in high-temperature superconductors known as cuprates, electrons bind together in pairs. The energy required to pull a pair apart -- called the energy gap -- is different in different directions; a plot of energy vs. direction forms a cloverleaf pattern. The explanation for this so-called "pseudogap" has so far eluded physicists.

The new work finds that in a cuprate that is not a superconductor at any temperature the same cloverleaf-shaped energy gap appears. The surprise for physicists is that the same materials in two very different states apparently have identical energy-gap structures.

"This may provide a key to understanding the superconducting phenomenon," said J.C. Séamus Davis, Cornell professor of physics, who collaborated in the work with Brookhaven physicist Tonica Valla. "This is the first time that it has been possible to measure the electronic structure of this very important material. The big surprise is that we go to this state where it's not superconducting, and we measure the electronic structure, and lo and behold, it's the same [as the superconductor]."

Their experiments were described Nov. 16 in the online journal Science Express and will appear in a future print edition of Science.

Superconductors conduct electricity with virtually no resistance. The phenomenon was first discovered in materials cooled to near absolute zero by immersion in liquid helium. Certain oxides of copper called cuprates that have been "doped" with small amounts of other elements become superconducting at temperatures up to 134 kelvins (degrees above absolute zero) or more, depending on pressure. These materials can be cooled with much less expensive liquid nitrogen and are in wide use in industry.

"Doping" disrupts the crystal structure of the copper oxide, creating "holes" where electrons ought to be, and this somehow facilitates superconductivity. Physicists have been puzzled by the fact that at a certain low level of doping, many cuprates cease to superconduct, yet at levels above and below this, superconductivity returns.

Valla, Davis and co-workers studied a version of a cuprate known as LBCO that ceases to superconduct when just one-eighth of its electrons have been removed. Previous measurements have shown that in this material the electrons arrange themselves in alternating "stripes" about four atoms wide, and this somehow seems to inhibit superconductivity.

The researchers studied samples cooled to near absolute zero -- where the material is still not a superconductor -- to observe the simplest or "ground" state. This was, the researchers said, the first measurement of the electronic structure of a cuprate in which the material's superconductivity did not interfere.

Valla's group measured the energy and momentum of the electrons in the non-superconducting LBCO by photoemission spectroscopy, in which X-rays are used to knock electrons off the surface for measurement. Davis and colleagues at Cornell studied a piece of the same crystal with a specially built scanning tunneling microscope so sensitive that it can detect the arrangement of electrons in the material. They were amazed to find that in both kinds of measurements, all low-energy electronic signatures were the same in the "striped" material as in superconducting cuprates.

Valla speculated that the difference lies in the way electrons form pairs, that they might sometimes pair too strongly for superconductivity to work. Davis declined to speculate, simply saying, "The electronic structure we observe ... appears to indicate that the 'striped' state is intimately related to the superconducting state -- perhaps they are two sides of the same coin."

It will be up to theorists, he said, to revise their theories to account for these results.

The research was supported by the U.S. Department of Energy, the Office of Naval Research and Cornell.


TOPICS: News/Current Events
KEYWORDS: high; stripes; superconductivity; temperature

1 posted on 12/05/2006 4:04:24 PM PST by blam
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To: blam
The big surprise is that we go to this state where it's not superconducting, and we measure the electronic structure, and lo and behold, it's the same [as the superconductor]."

All things being equal you check the equipment first.
2 posted on 12/05/2006 4:11:02 PM PST by kinoxi
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To: blam
... experiments have shown that in high-temperature superconductors known as cuprates, electrons bind together in pairs. ... in a cuprate that is not a superconductor at any temperature ...

We can then determine that a cuprate is something with copper in it which may or may not be superconducting at some temperature or any temperature!

3 posted on 12/05/2006 4:15:39 PM PST by Ken522
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To: Ken522

I think cuprate might be used as a generic term for superconductor here.


4 posted on 12/05/2006 4:18:55 PM PST by kinoxi
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To: kinoxi

Cuprate, meaning a chemical class of superconductors, as they have cuprates in their formulas.


5 posted on 12/05/2006 4:32:39 PM PST by right-wingin_It
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To: right-wingin_It

Thank you for correcting me.


6 posted on 12/05/2006 4:38:55 PM PST by kinoxi
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To: RightWhale

Ping.


7 posted on 12/05/2006 4:44:38 PM PST by blam (Old Sub Sailor - SS-368)
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To: right-wingin_It; kinoxi

The cuprate is about $1.70 at most coffee shops, but then you get free refills so I guess it depends on how long you stay.


8 posted on 12/05/2006 4:46:14 PM PST by who_would_fardels_bear
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To: blam

Thanks. Saw this. Superconductivity will eventually be in everything. Too bad about the Superconducting Supercollider. We will probably never again have the chance to build that, but who knows, something even better could come along.


9 posted on 12/05/2006 4:47:30 PM PST by RightWhale (RTRA DLQS GSCW)
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To: blam

superconductivity bump for later.......


10 posted on 12/05/2006 4:53:18 PM PST by indthkr
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To: blam
134 kelvins

This is written by Cornell? Someone needs a talking to. The kelvin (symbol K) is never plural. The unit is singular. It should never be written as 'degrees kelvin', either. Nor should it have a little circular 'degree' symbol. It is just plain kelvin. 134 kelvin or 134 K. http://physics.nist.gov/cuu/Units/kelvin.html

11 posted on 12/05/2006 5:01:53 PM PST by Right Wing Assault ("..this administration is planning a 'Right Wing Assault' on values and ideals.." - John Kerry)
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To: Right Wing Assault

Oops.

http://physics.nist.gov/cuu/Units/kelvin.html


12 posted on 12/05/2006 5:03:25 PM PST by Right Wing Assault ("..this administration is planning a 'Right Wing Assault' on values and ideals.." - John Kerry)
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The new work finds that in a cuprate that is not a superconductor at any temperature the same cloverleaf-shaped energy gap appears. The surprise for physicists is that the same materials in two very different states apparently have identical energy-gap structures.

13 posted on 06/20/2007 10:41:02 PM PDT by SunkenCiv (Time heals all wounds, particularly when they're not yours. Profile updated June 20, 2007.)
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