Closing in on a theory of superconductivity - GoFuckYourself.com

Juicy D. Links · 03-15-2004, 04:23 PM

Interesting read

Theorists have put forward many theories to explain high-temperature superconductivity in materials containing layers of copper oxide. A team of experimenters from McMaster University in Canada and the Brookhaven National Laboratory in the US has now ruled out two of these theories and presented new evidence that magnetic correlations between pairs of electrons is responsible for superconductivity in the cuprates (J Hwang et al. 2004 Nature 427 714).

Superconductivity is the complete absence of electrical resistance in a material and is observed in certain materials when they are cooled to below their superconducting transition temperature. Physicists agree that superconductivity relies on getting electrons to overcome their mutual Coulomb repulsion and form "Cooper pairs". In the Bardeen-Cooper-Schrieffer (BCS) theory of low-temperature superconductivity, the electrons are held together as a result of their interactions with phonons - lattice vibrations - in the material.

Self-energy spectrum

However, the BCS theory can not explain the behaviour of high-temperature superconductors - which were discovered in 1986 and can have transition temperatures as high as 138 Kelvin. Now, Thomas Timusk of McMaster and colleagues have measured the optical self-energy spectrum of a bismuth-based cuprate superconductor known as Bi-2212. The McMaster-Brookhaven team found that the spectrum was broad and featureless above 88 Kelvin, the superconducting transition temperature of the material. However, a sharp peak appeared in the spectrum below this temperature (see figure).

According to the team, the results rule out theories based on phonons and the creation of a magnetic resonance state in the material, but they are consistent with the "magnetic-pairing" model of high-temperature superconductivity. "The results show that the magnetic resonance that has been the subject of a large number of recent papers does not by itself cause high-temperature superconductivity," says Timusk. "Moreover, a hypothetical phonon at the same energy as the magnetic resonance cannot be the cause either."

Timusk adds that the team's approach could be used to analyse excitations in a wide range of other high-temperature superconductors and "exotic" materials.

Fu-Q · 03-15-2004, 04:25 PM

do you have a link?

Crazy_Canuck · 03-15-2004, 04:27 PM

I'm not sure that's all written in English.
Cool stuff

Juicy D. Links · 03-15-2004, 04:27 PM

Quote:

Originally posted by Fu-Q
do you have a link?

http://physicsweb.org/article/news/8/2/10

Fu-Q · 03-15-2004, 04:27 PM

thanks

DTK · 03-15-2004, 04:38 PM

Quote:

Originally posted by Crazy_Canuck

Cool stuff

Indeed....

hoe_vender · 03-15-2004, 05:30 PM

good to know

DTK · 03-15-2004, 05:44 PM

^
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Post bot, eh?

03-15-2004, 04:23 PM	#1
Juicy D. Links So Fucking Banned Industry Role: Join Date: Apr 2001 Location: N.Y. -Long Island -- Posts: 122,992	Closing in on a theory of superconductivity Interesting read Theorists have put forward many theories to explain high-temperature superconductivity in materials containing layers of copper oxide. A team of experimenters from McMaster University in Canada and the Brookhaven National Laboratory in the US has now ruled out two of these theories and presented new evidence that magnetic correlations between pairs of electrons is responsible for superconductivity in the cuprates (J Hwang et al. 2004 Nature 427 714). Superconductivity is the complete absence of electrical resistance in a material and is observed in certain materials when they are cooled to below their superconducting transition temperature. Physicists agree that superconductivity relies on getting electrons to overcome their mutual Coulomb repulsion and form "Cooper pairs". In the Bardeen-Cooper-Schrieffer (BCS) theory of low-temperature superconductivity, the electrons are held together as a result of their interactions with phonons - lattice vibrations - in the material. Self-energy spectrum However, the BCS theory can not explain the behaviour of high-temperature superconductors - which were discovered in 1986 and can have transition temperatures as high as 138 Kelvin. Now, Thomas Timusk of McMaster and colleagues have measured the optical self-energy spectrum of a bismuth-based cuprate superconductor known as Bi-2212. The McMaster-Brookhaven team found that the spectrum was broad and featureless above 88 Kelvin, the superconducting transition temperature of the material. However, a sharp peak appeared in the spectrum below this temperature (see figure). According to the team, the results rule out theories based on phonons and the creation of a magnetic resonance state in the material, but they are consistent with the "magnetic-pairing" model of high-temperature superconductivity. "The results show that the magnetic resonance that has been the subject of a large number of recent papers does not by itself cause high-temperature superconductivity," says Timusk. "Moreover, a hypothetical phonon at the same energy as the magnetic resonance cannot be the cause either." Timusk adds that the team's approach could be used to analyse excitations in a wide range of other high-temperature superconductors and "exotic" materials.

03-15-2004, 04:25 PM	#2
Fu-Q Confirmed User Join Date: Jul 2003 Location: Seattle Posts: 1,546	do you have a link? __________________ AIM - X8U ICQ - 195301080

03-15-2004, 04:27 PM	#3
Crazy_Canuck Confirmed User Join Date: Dec 2002 Location: Ottawa Posts: 124	I'm not sure that's all written in English. Cool stuff __________________ SIG TOO BIG! Maximum 120x60 button and no more than 3 text lines of DEFAULT SIZE and COLOR. Unless your sig is for a GFY top banner sponsor, then you may use a 624x80 instead of a 120x60.

03-15-2004, 04:27 PM	#5
Fu-Q Confirmed User Join Date: Jul 2003 Location: Seattle Posts: 1,546	thanks __________________ AIM - X8U ICQ - 195301080

03-15-2004, 05:30 PM	#7
hoe_vender Confirmed User Join Date: Dec 2003 Location: Lincoln, NE Posts: 2,018	good to know __________________ ICQ #286508534

03-15-2004, 05:44 PM	#8
DTK Confirmed User Industry Role: Join Date: Feb 2002 Location: The 510 Posts: 4,545	^ ^ ^ ^ ^ ^ Post bot, eh? __________________ Arguing whether the Democratic or Republican party is better is like debating which steaming pile of shit is slightly less stinky.