Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Dopants dramatically alter electronic structure of superconductor

18.02.2013
Findings explain unusual properties, but complicate search for universal theory

Over the last quarter century, scientists have discovered a handful of materials that can be converted from magnetic insulators or metals into "superconductors" able to carry electrical current with no energy loss-an enormously promising idea for new types of zero-resistance electronics and energy-storage and transmission systems.

At present, a key step to achieving superconductivity (in addition to keeping the materials very cold) is to substitute a different kind of atom into some positions of the "parent" material's crystal framework. Until now, scientists thought this process, called doping, simply added more electrons or other charge carriers, thereby rendering the electronic environment more conducive to the formation of electron pairs that could move with no energy loss if the material is held at a certain chilly temperature.

Now, new studies of an iron-based superconductor by an international team of scientists - including physicists from the U.S. Department of Energy's Brookhaven National Laboratory and Cornell University - suggest that the story is somewhat more complicated. Their research, published online in Nature Physics February 17, 2013,* demonstrates that doping, in addition to adding electrons, dramatically alters the atomic-scale electronic structure of the parent material, with important consequences for the behavior of the current-carrying electrons.

"The key observation - that dopant atoms introduce elongated impurity states which scatter electrons in the material in an asymmetric way - helps explain most of the unusual properties," said J.C. Séamus Davis, the study's lead author, who directs the Center for Emergent Superconductivity at Brookhaven Lab and is also the J.G. White Distinguished Professor of Physical Sciences at Cornell University. "Our findings provide a new starting point for theorists trying to grapple with how these materials work, and could potentially point to new ways to design superconductors with improved properties," he said.

The researchers used a technique developed by Davis called spectroscopic imaging scanning tunneling microscopy to visualize the electronic properties around individual dopant atoms in the parent material, and to simultaneously monitor how electrons scatter around these dopants (in this case, cobalt).

Earlier studies had shown that certain electronic properties of the non-superconducting "parent" material had a strong directional dependence - for example, electrons were able to move more easily in one direction through the crystal than in the perpendicular direction. However, in those studies, the signal of a strong directional dependence only appeared when the scientists put the dopants into the material, and got stronger the more dopants they added.

Before this, the assumption was that dopants simply added electrons, and that the material's properties - including the emergence of superconductivity - were due to some intrinsic characteristic (for example, the alternating alignments of electron spins on adjacent atoms) that resulted in a directional dependence.

"But the emergence of directional dependence of electronic properties as more dopants are added suggests that the strong directionality is a result of the dopants, not an intrinsic property of the material," Davis said. "We decided to test this idea by directly imaging what each dopant atom does to the nearby atomic-level electronic structure in these materials."

According to Davis, the current paper reports two very clear results:

1) At each cobalt dopant atom, there is an elongated impurity state-a quantum mechanical state bound to the cobalt atom-that aligns in a particular direction (the same for each cobalt atom) relative to the overall crystal. 2) These oblong, aligned impurity states scatter the current-carrying electrons away from the impurity state in an asymmetric way - similar to the way ripples of water would propagate asymmetrically outward from an elongated stick thrown into a pond, rather than forming the circular pattern produced by a pebble.

"These direct observational findings explain most of the outstanding mysteries about how the electrical current moves through these materials - for example, with greater ease perpendicular to the direction you would expect based solely on the characteristics of the parent material," Davis said. "The results show that the dopants actually do dramatic things to the electronic structure of the parent material."

"It's possible that what we've found could be similar to an effect dopants had on early semiconductors," Davis said. "Early versions of these materials, though useful, had nowhere near the performance as those developed after the 1970s, when scientists at Bell Labs figured out a way to move the dopant atoms far away from the electrons so they wouldn't mess up the electronic structure." That advance made possible all the microelectronics we now use every day, including cell phones, he said.

"If we find out the dopant atoms are doing something we don't want in the iron and even copper superconductors, maybe we can find a way to move them away from the active electrons to make more useful materials."

Brookhaven's role in this research was supported by the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center headquartered at Brookhaven National Laboratory. Additional funding was provided by the DOE Office of Science (Ames Laboratory), the National Science Foundation, the U.K. Engineering and Physical Sciences Research Council, the Scottish Funding Council, and the Netherlands Organization for Scientific Research.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization. Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more or follow Brookhaven Lab on Twitter.

Karen McNulty Walsh | EurekAlert!
Further information:
http://www.bnl.gov

More articles from Physics and Astronomy:

nachricht Australian technology installed on world’s largest single-dish radio telescope
26.09.2016 | International Centre for Radio Astronomy Research (ICRAR)

nachricht How to merge two black holes in a simple way
26.09.2016 | Plataforma SINC

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

Im Focus: Complex hardmetal tools out of the 3D printer

For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.

Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...

Im Focus: Launch of New Industry Working Group for Process Control in Laser Material Processing

At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.

In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...

Im Focus: New laser joining technologies at ‘K 2016’ trade fair

Every three years, the plastics industry gathers at K, the international trade fair for plastics and rubber in Düsseldorf. The Fraunhofer Institute for Laser Technology ILT will also be attending again and presenting many innovative technologies, such as for joining plastics and metals using ultrashort pulse lasers. From October 19 to 26, you can find the Fraunhofer ILT at the joint Fraunhofer booth SC01 in Hall 7.

K is the world’s largest trade fair for the plastics and rubber industry. As in previous years, the organizers are expecting 3,000 exhibitors and more than...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Experts from industry and academia discuss the future mobile telecommunications standard 5G

23.09.2016 | Event News

ICPE in Graz for the seventh time

20.09.2016 | Event News

Using mathematical models to understand our brain

16.09.2016 | Event News

 
Latest News

Stronger turbine blades with molybdenum silicides

26.09.2016 | Materials Sciences

Scientists Find Twisting 3-D Raceway for Electrons in Nanoscale Crystal Slices

26.09.2016 | Materials Sciences

Lowering the Heat Makes New Materials Possible While Saving Energy

26.09.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>