Featured Research

from universities, journals, and other organizations

Atomic-scale visualization of electron pairing in iron superconductors

May 3, 2012
DOE/Brookhaven National Laboratory
By measuring how strongly electrons are bound together to form Cooper pairs in an iron-based superconductor, scientists provide direct evidence supporting theories in which magnetism holds the key to this material's ability to carry current with no resistance.

Data supports role of magnetism in iron-based superconductors: The height of each dot in this image represents the superconducting energy gap — a measure of the strength of electron pairing — for electrons moving at a particular momentum (speed in a given direction) on each electronic band (red and yellow rings) of a particular iron superconductor. The data show that the magnitude of the gap (height of the dots) varies by its momentum (position along the base plane) and the band it is on — which is exactly what was predicted by theories in which magnetism plays a primary role in the emergence of superconductivity. The results therefore strengthen confidence that those theories may help scientists discover or design new superconductors.
Credit: Image courtesy of DOE/Brookhaven National Laboratory

By measuring how strongly electrons are bound together to form Cooper pairs in an iron-based superconductor, scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, Cornell University, St. Andrews University, and collaborators provide direct evidence supporting theories in which magnetism holds the key to this material's ability to carry current with no resistance. Because the measurements take into account the electronic bands and directions in which the electrons are traveling, which was central to testing the theoretical predictions, this research strengthens confidence that this type of theory may one day be used to identify or design new materials with improved properties -- namely, superconductors operating at temperatures far higher than today's.

The findings are published in the May 4, 2012 issue of Science.

"In the best possible world you would be able to take this theory and plug in different chemical elements until you find a combination that should work as a superconductor at higher temperatures," said team leader Séamus Davis, Director of the Center for Emergent Superconductivity at Brookhaven and the J.G. White Distinguished Professor of Physical Sciences at Cornell University. Such materials could be used for real world, energy-saving technologies, such as zero-loss power transmission lines, without the need for expensive coolants.

Scientists have been trying to understand the mechanism underlying so-called "high-temperature" superconductivity ever since discovering materials that could carry current with no resistance at temperatures somewhat above the operating realm of conventional superconductors, which must be chilled to near absolute zero (0 kelvin, or -273° Celsius). Though still mighty chilly, these high-Tc materials' operating temperatures -- some as high as 145K (-130° C) -- offer hope that such materials could one day be designed to operate at room temperature.

One key to superconductivity is the formation of electron pairs. Scientists hypothesized that if these negatively charged particles have their magnetic moments pointing in opposite directions, they could overcome their mutual repulsion to join forces in so-called Cooper pairs -- thus carrying current with no loss.

"Many people suspected you could take materials that naturally have alternating magnetic moments on adjacent electrons -- antiferromagnetic materials -- and convert them into superconductors," Davis said. But to prove this conjecture hasn't been possible with copper-based, or cuprate, superconductors -- the first high-Tc superconductors discovered starting some 25 years ago. "You can make a robust antiferromagnetic cuprate insulator, but in that state it's hard to get the magnetic electrons to pair and then move around and make a superconductor," Davis said.

Then, in 2008, when iron-based superconductors were discovered, the idea that magnetism plays a role in high-Tc superconductivity was revived. But determining that role was a very complex problem.

"In each iron atom there are five magnetic electrons, not just one," Davis said. "And each, as it moves around the crystal, does so in a separate electronic band. In order to find out if the magnetic interactions between electrons are generating the superconductivity, you have to measure what's called the anisotropic energy gap -- how strongly bound together the electrons are in a pair -- depending on the electrons' directions on the different electronic bands."

Theorists Dung-Hai Lee of the University of California at Berkeley, Peter Hirschfeld of the University of Florida, and Andrey Chubukov of the University of Wisconsin among others had developed different versions of a theory that predicts what those measurements should be if magnetism were the mechanism for superconductivity.

"It was our job to test those predictions," Davis said. But at first, the techniques didn't exist to make the measurements. "We had to invent them," Davis said.

Two scientists working with Davis, Milan P. Allan of Brookhaven, Cornell, and the University of Saint Andrews (where Davis also teaches) and Andreas W. Rost of Cornell and St. Andrews -- the lead authors on the paper -- figured out how to do the experiments and identified an iron-based material (lithium iron arsenide) in which to test the predictions.

Their method, multi-band Bogoliubov quasiparticle scattering interference, found the "signature" predicted by the theorists:

"The strength of the 'glue' holding the pairs together is different on the different bands, and on each band it depends on the direction that the electrons are traveling -- with the pairing usually being stronger in a given direction than at 45° to that direction," Davis said.

"This is the first experimental evidence direct from the electronic structure in support of the theories that the mechanism for superconductivity in iron-based superconductors is due primarily to magnetic interactions," he said.

The next step is to use the same technique to determine whether the theory holds true for other iron superconductors. "We and others are working on that now," Davis said.

If those experiments show that the theory is indeed correct, the model could then be used to predict the properties of other elements and combinations -- and ideally point the way toward engineering new materials and higher-temperature superconductors.

Story Source:

The above story is based on materials provided by DOE/Brookhaven National Laboratory. Note: Materials may be edited for content and length.

Journal Reference:

  1. M. P. Allan, A. W. Rost, A. P. Mackenzie, Y. Xie, J. C. Davis, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, T.- M. Chuang. Anisotropic Energy Gaps of Iron-Based Superconductivity from Intraband Quasiparticle Interference in LiFeAs. Science, 2012; 336 (6081): 563 DOI: 10.1126/science.1218726

Cite This Page:

DOE/Brookhaven National Laboratory. "Atomic-scale visualization of electron pairing in iron superconductors." ScienceDaily. ScienceDaily, 3 May 2012. <www.sciencedaily.com/releases/2012/05/120503142542.htm>.
DOE/Brookhaven National Laboratory. (2012, May 3). Atomic-scale visualization of electron pairing in iron superconductors. ScienceDaily. Retrieved April 24, 2014 from www.sciencedaily.com/releases/2012/05/120503142542.htm
DOE/Brookhaven National Laboratory. "Atomic-scale visualization of electron pairing in iron superconductors." ScienceDaily. www.sciencedaily.com/releases/2012/05/120503142542.htm (accessed April 24, 2014).

Share This

More Matter & Energy News

Thursday, April 24, 2014

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Next Stop America for France's TGV?

Next Stop America for France's TGV?

Reuters - Business Video Online (Apr. 24, 2014) — General Electric keeps quiet on reports it's in talks to buy French turbine and train maker Alstom. Ivor Bennett reports on what could be an embarrassing rumour for the French government, with business-friendly reforms proving a hard sell. Video provided by Reuters
Powered by NewsLook.com
Raw: Obama Plays Soccer With Japanese Robot

Raw: Obama Plays Soccer With Japanese Robot

AP (Apr. 24, 2014) — President Obama briefly played soccer with a robot during his visit to Japan on Thursday. The President has been emphasizing technology along with security concerns during his visit. (April 24) Video provided by AP
Powered by NewsLook.com
Obama Encourages Japanese Student-Scientists

Obama Encourages Japanese Student-Scientists

AP (Apr. 24, 2014) — President Obama spoke with student innovators in Japan and urged them to take part in increased opportunities for student exchanges with the US. (April 24) Video provided by AP
Powered by NewsLook.com
UN Joint Mission Starts Removing Landmines in Cyprus

UN Joint Mission Starts Removing Landmines in Cyprus

AFP (Apr. 23, 2014) — The UN mission in Cyprus (UNFICYP) led a mine clearance demonstration on Wednesday in the UN-controlled buffer zone where demining operations are being conducted near the Cypriot village of Mammari. Duration: 01:00 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.


Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News


Free Subscriptions

Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile

Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?

Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins