Featured Research

from universities, journals, and other organizations

Dopants dramatically alter electronic structure of superconductor

February 17, 2013
DOE/Brookhaven National Laboratory
Doping dramatically alters the atomic-scale electronic structure of the parent of a high-temperature superconductor, with important consequences for the behavior of the current-carrying electrons, according to new research. The findings could potentially point to new ways to design superconductors with improved properties.

Scientists have found that the substitution of cobalt atoms into the crystal framework of an iron-based material—which is required to convert the material from a magnet into a superconductor—also introduces elongated impurity states at each cobalt atom (note the directional alignment of "twin" peaks around each cobalt atom in the electronic structure map). These elongated impurities then scatter electrons in an asymmetric way that explains many of the material's unusual properties, and could eventually lead to the design of new types of superconductors for practical applications in energy transmission and storage.
Credit: Image courtesy of DOE/Brookhaven National Laboratory

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.

Related Articles

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."

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, T-M. Chuang, F. Massee, Yang Xie, Ni Ni, S. L. Bud’ko, G. S. Boebinger, Q. Wang, D. S. Dessau, P. C. Canfield, M. S. Golden & J. C. Davis. Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1−xCox)2As2. Nature Physics, 17 February 2013 DOI: 10.1038/nphys2544

Cite This Page:

DOE/Brookhaven National Laboratory. "Dopants dramatically alter electronic structure of superconductor." ScienceDaily. ScienceDaily, 17 February 2013. <www.sciencedaily.com/releases/2013/02/130217134253.htm>.
DOE/Brookhaven National Laboratory. (2013, February 17). Dopants dramatically alter electronic structure of superconductor. ScienceDaily. Retrieved December 21, 2014 from www.sciencedaily.com/releases/2013/02/130217134253.htm
DOE/Brookhaven National Laboratory. "Dopants dramatically alter electronic structure of superconductor." ScienceDaily. www.sciencedaily.com/releases/2013/02/130217134253.htm (accessed December 21, 2014).

Share This

More From ScienceDaily

More Matter & Energy News

Sunday, December 21, 2014

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Building Google Into Cars

Building Google Into Cars

Reuters - Business Video Online (Dec. 19, 2014) — Google's next Android version could become the standard that'll power your vehicle's entertainment and navigation features, Reuters has learned. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
AP Review: Nikon D750 and GoPro Hero 4

AP Review: Nikon D750 and GoPro Hero 4

AP (Dec. 19, 2014) — What to buy an experienced photographer or video shooter? There is some strong gear on the market from Nikon and GoPro. The AP's Ron Harris takes a closer look. (Dec. 19) Video provided by AP
Powered by NewsLook.com
Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Buzz60 (Dec. 19, 2014) — A double-amputee makes history by becoming the first person to wear and operate two prosthetic arms using only his mind. Jen Markham has the story. Video provided by Buzz60
Powered by NewsLook.com
Navy Unveils Robot Fish

Navy Unveils Robot Fish

Reuters - Light News Video Online (Dec. 18, 2014) — The U.S. Navy unveils an underwater device that mimics the movement of a fish. Tara Cleary reports. Video provided by Reuters
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:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

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