Study helps explain behavior of latest high-temp superconductors

May 03, 2011

A Rice University-led team of physicists this week offered up one of the first theoretical explanations of how two dissimilar types of high-temperature superconductors behave in similar ways.

The research appears online this week in the journal . It describes how the of electrons in two dissimilar families of iron-based materials called "pnictides" (pronounced: NICK-tides) could give rise to superconductivity. One of the parent families of pnictides is a metal and was discovered in 2008; the other is an and was discovered in late 2010. Experiments have shown that each material, if prepared in a particular way, can become a superconductor at roughly the same temperature. This has left theoretical physicists scrambling to determine what might account for the similar behavior between such different compounds.

Rice physicist Qimiao Si, the lead researcher on the new paper, said the explanation is tied to subtle differences in the way iron atoms are arranged in each material. The pnictides are laminates that contain layers of iron separated by layers of other compounds. In the newest family of , Chinese scientists found a way to selectively remove iron atoms and leave an orderly pattern of "vacancies" in the iron layers.

Si, who learned about the discovery of the new insulating compounds during a visit to China in late December, suspected that the explanation for the similar behavior between the new and old compounds could lie in the collective way that electrons behave in each as they are cooled to the point of superconductivity. His prior work had shown that the arrangement of the iron atoms in the older materials could give rise to of the magnetic moments, or "spins," of electrons. These collective behaviors, or "quasi-localizations," have been linked to high-temperature superconductivity in both pnictides and other high-temperature superconductors.

"The reason we got there first is we were in a position to really quickly incorporate the effect of vacancies in our model," Si said. "Intuitively, on my flight back (from China last Christmas), I was thinking through the calculations we should begin doing."

Si conducted the calculations and analyses with co-authors Rong Yu, postdoctoral research associate at Rice, and Jian-Xin Zhu, staff scientist at Los Alamos National Laboratory.

"We found that ordered vacancies enhance the tendency of the electrons to lock themselves some distance away from their neighbors in a pattern that physicists call 'Mott localization,' which gives rise to an insulating state," Yu said. "This is an entirely new route toward Mott localization."

By showing that merely creating ordered vacancies can prevent the material from being electrical conductors like their relatives, the researchers concluded that even the metallic parents of the iron pnictides are close to Mott localization.

"What we are learning by comparing the new materials with the older ones is that these quasi-localized spins and the interactions among them are crucial for superconductivity, and that's a lesson that can be potentially applied to tell experimentalists what is good for raising the transition temperature in new families of compounds," Zhu said.

Superconductivity occurs when pair up and flow freely through a material without any loss of energy due to resistance. This most often occurs at extremely low temperatures, but compounds like the pnictides and others become superconductors at higher temperatures -- close to or above the temperature of liquid nitrogen -- which creates the possibility that they could be used on an industrial scale. One impediment to their broader use has been the struggle to precisely explain what causes them to become superconductors in the first place. The race to find that has been called the biggest mystery in modern physics.

"The new superconductors are arguably the most important iron-based materials that have been discovered since the initial discovery of iron pnictide high-temperature superconductors in 2008," Si said. "Our theoretical results provide a natural link between the new and old iron-based , thereby suggesting a universal origin of the superconductivity in these materials."

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rawa1
not rated yet May 04, 2011
what causes them to become superconductors in the first place. The race to find that has been called the biggest mystery in modern physics
It's the mutual compression of electrons - if we would compress the electrons inside of pipe, the core of pipe would become superconductive. Because inside of squeezed electrons their repulsive forces overlap mutually in such way, the geometric constrains for electron motion effectively disappear. At the case of superconductors, the electrons are compressed with attractive forces of positively charged vacancies, i.e. the "holes" within superconductor lattice. I presume, such mystery could be solved before many years, because it's not difficult to understand at all.
Na_Reth
not rated yet May 04, 2011
They deliberately hold back this kind of technology so that we wont invent super capacitors that will make most today's tech obsolete.
Bog_Mire
5 / 5 (1) May 04, 2011
They deliberately hold back this kind of technology so that we wont invent super capacitors that will make most today's tech obsolete.


who are "they"?
KBK
not rated yet May 04, 2011
The ever ambiguous 'they', you know, 'them'.

Humor aside, look up the comments of the ex-head of Lockheed Martin's Skunkworks, Ben Rich.

If you are serious about knowing exactly 'they' are, look up his comments. IIRC, he was dying of Caner and had nothing to loose. So he began laying out the truths he was involved in.

Aliens, FTL craft, things that would be off the scale, with regard to the average person's capacity to accept.

In essence, their are far greater levels of science and social/technical groupings than the common man, (scientifically trained or not) is aware of.

If acceptance of such points (once discovered) is an issue, with regard to your psychology and attendant physiology, understand that this is the barrier that holds you back, not the reality of those societal and technical levels.

More of the common public is waking to these understandings.. so the speed of the information and societal controls are attempting to move slightly faster.

Look around you.

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