Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Argonne scientists discover new magnetic phase in iron-based superconductors


Scientists at the U.S. Department of Energy’s Argonne National Laboratory have discovered a previously unknown phase in a class of superconductors called iron arsenides. This sheds light on a debate over the interactions between atoms and electrons that are responsible for their unusual superconductivity.

“This new magnetic phase, which has never been observed before, could have significant implications for our understanding of unconventional superconductivity,” said Ray Osborn, an Argonne physicist and coauthor on the paper.

A neutron diffraction image giving evidence for the new magnetic phase in iron-based superconductors discovered by Argonne scientists. It shows the scattering results from a sample of barium iron arsenide with sodium ions added to 24% of the barium sites. Nematic order sets in below 90 K (about -300°F), but four-fold symmetry is restored below 40 K (-387°F). The resulting atomic and magnetic structures are illustrated in the figure on the right, in which the blue spheres represent iron atoms and the red arrows show the direction of their magnetic moments. Credit: Image by Jared Allred / Argonne National Laboratory

Scientists and engineers are fascinated with superconductors because they are capable of carrying electric current without any resistance. This is unique among all conductors: even good ones, like the copper wires used in most power cords, lose energy along the way. Why don’t we use superconductors for every power line in the country, then? Their biggest drawback is that they must be cooled to very, very cold temperatures to work. Also, we do not fully understand how the newest types, called unconventional superconductors, work. Researchers hope that by figuring out the theory behind these superconductors, we could raise the temperature at which they work and harness their power for a wide range of new technologies.

The theory behind older, “conventional” superconductors is fairly well understood. Pairs of electrons, which normally repel each other, instead bind together by distorting the atoms around them and help each other travel through the metal. (In a plain old conductor, these electrons bounce off the atoms, producing heat). In “unconventional” superconductors, the electrons still form pairs, but we don’t know what binds them together.

Superconductors are notably finicky; in order to get to the superconducting phase—where electricity flows freely—they need a lot of coddling. The iron arsenides the researchers studied are normally magnetic, but as you add sodium to the mix, the magnetism is suppressed and the materials eventually become superconducting below roughly -400 degrees Fahrenheit.

Magnetic order also affects the atomic structure. At room temperature, the iron atoms sit on a square lattice, which has four-fold symmetry, but when cooled below the magnetic transition temperature, they distort to form a rectangular lattice, with only two-fold symmetry. This is sometimes called “nematic order.” It was thought that this nematic order persists until the material becomes superconducting—until this result. 

The Argonne team discovered a phase where the material returns to four-fold symmetry, rather than two-fold, close to the onset of superconductivity. (See diagram).

“It is visible using neutron powder diffraction, which is exquisitely sensitive, but which you can only perform at this resolution in a very few places in the world,” Osborn said. Neutron powder diffraction reveals both the locations of the atoms and the directions of their microscopic magnetic moments.

The reason why the discovery of the new phase is interesting is that it may help to resolve a long-standing debate about the origin of nematic order. Theorists have been arguing whether it is caused by magnetism or by orbital ordering.

The orbital explanation posits that electrons like to sit in particular d orbitals, driving the lattice into the nematic phase. Magnetic models, on the other hand (developed by study co-authors Ilya Eremin and Andrey Chubukov at the Institut für Theoretische Physik in Germany and the University of Wisconsin-Madison, respectively) suggest that magnetic interactions are what drive the two-fold symmetry—and that they are the key to the superconductivity itself. Perhaps what binds the pairs of electrons together in iron arsenide superconductors is magnetism.

“Orbital theories do not predict a return to four-fold symmetry at this point,” Osborn said, “but magnetic models do.”

“So far, this effect has only been observed experimentally in these sodium-doped compounds,” he said, “but we believe it provides evidence for a magnetic explanation of nematic order in the iron arsenides in general.”

It could also affect our understanding of superconductivity in other types of superconductors, such as the copper oxides, where nematic distortions have also been seen, Osborn said.

The paper, titled “Magnetically driven suppression of nematic order in an iron-based superconductor,” was published today in Nature Communications.

Other coauthors on the paper were Argonne scientists Sevda Avci (now at Afyon Kocatepe University in Turkey), Omar Chmaissem (a joint appointment with Northern Illinois University), Jared M. Allred, Stephan Rosenkranz, Daniel Bugaris, Duck Young Chung, John-Paul Castellan, John Schlueter, Helmut Claus and Mercouri Kanatzidis (a joint appointment with Northwestern University); and Dmitry Khalyavin, Pascal Manuel and Aziz Daoud-Aladine at the ISIS Pulsed Neutron and Muon Source at the Rutherford Appleton Laboratory in Oxfordshire, U.K.

Funding for the research was provided by the U.S. Department of Energy’s Office of Science. The neutron powder diffraction was performed at ISIS.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

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, visit

Jared Sagoff | Eurek Alert!
Further information:

Further reports about: ISIS Magnetic Neutron copper energy powder superconductors temperature

More articles from Power and Electrical Engineering:

nachricht Fluorescent holography: Upending the world of biological imaging
25.10.2016 | Colorado State University

nachricht Did you know that infrared heating is an essential part of automotive manufacture?
25.10.2016 | Heraeus Noblelight GmbH

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Ice shelf vibrations cause unusual waves in Antarctic atmosphere

25.10.2016 | Earth Sciences

Fluorescent holography: Upending the world of biological imaging

25.10.2016 | Power and Electrical Engineering

Etching Microstructures with Lasers

25.10.2016 | Process Engineering

More VideoLinks >>>