We have been able to comparethree separate materials working at the same approximate temperatures andsuggest structure that helps explain it.
Perhaps someday we will have afully satisfying solution to the problem. This is another incremental improvement.
Great work as we are now makingseveral materials that work at relatively high temperatures. Liquid nitrogen temperatures are more thatgood enough for what we want to do. Roomtemperature was always dreaming in Technicolor and actually unnecessary.
Study helps explain behavior of latest high-temp superconductors
by Staff Writers
A Rice University-led team of physicists this week offered up one of the firsttheoretical explanations of how two dissimilar types of high-temperaturesuperconductors behave in similar ways.
The research appears online this week in the journalPhysical Review Letters.It describes how the magnetic properties of electrons intwo dissimilar families of iron-based materials called "pnictides"(pronounced: NICK-tides) could give rise to superconductivity. One of theparent families of pnictides is a metal and was discovered in 2008; the otheris an insulator and was discovered in late 2010.
Experiments have shown that each material, if prepared in a particularway, can become a superconductor at roughly the same temperature. This has lefttheoretical physicists scrambling to determine what might account for thesimilar behavior between such different compounds.
Rice physicist Qimiao Si, the lead researcher on the new paper, saidthe explanation is tied to subtle differences in the way iron atoms arearranged in each material. The pnictides are laminates that contain layers ofiron separated by layers of other compounds.
In the newest family of insulating materials, Chinese scientists founda 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 compoundsduring a visit to China in late December, suspected that the explanation forthe similar behavior between the new and old compounds could lie in thecollective way that electrons behave in each as they are cooled to the point ofsuperconductivity.
His prior work had shown that the arrangement of the iron atoms in theolder materials could give rise to collective behavior of the magnetic moments,or "spins," of electrons.
These collective behaviors, or "quasi-localizations," havebeen linked to high-temperature superconductivity in both pnictides and otherhigh-temperature superconductors.
"The reason we got there first is we were in a position to reallyquickly incorporate the effect of vacancies in our model," Si said."Intuitively, on my flight back (from China
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 theelectrons to lock themselves some distance away from their neighbors in apattern that physicists call 'Mott localization,' which gives rise to aninsulating state," Yu said. "This is an entirely new route towardMott localization."
By showing that merely creating ordered vacancies can prevent thematerial from being electrical conductors like their relatives, the researchersconcluded that even the metallic parents of the iron pnictides are close toMott localization.
"What we are learning by comparing the new materials with theolder ones is that these quasi-localized spins and the interactions among themare crucial for superconductivity, and that's a lesson that can be potentiallyapplied to tell experimentalists what is good for raising the transitiontemperature in new families of compounds," Zhu said.
Superconductivity occurs when electrons pair up and flow freely througha material without any loss of energy due to resistance. This most often occursat extremely low temperatures, but compounds like the pnictides and othersbecome superconductors at higher temperatures - close to or above thetemperature of liquid nitrogen - which creates the possibility that they couldbe used on an industrial scale.
One impediment to their broader use has been the struggle to preciselyexplain what causes them to become superconductors in the first place. The raceto find that has been called the biggest mystery in modern physics.
"The new superconductors are arguably the most importantiron-based materials that have been discovered since the initial discovery ofiron pnictide high-temperature superconductors in 2008," Si said."Our theoretical results provide a natural link between the new and oldiron-based superconductors, thereby suggesting a universal origin of thesuperconductivity in these materials."
No comments:
Post a Comment