Science Current Events | Science News |

Atomic-scale visualization of electron pairing in iron superconductors

May 04, 2012

Findings support magnetic pairing theory that could lead to new improved superconductors

UPTON, NY - 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.

DOE/Brookhaven National Laboratory

Related Superconductors Current Events and Superconductors News Articles

Revealing the nature of magnetic interactions in manganese oxide
For nearly 60 years, scientists have been trying to determine how manganese oxide (MnO) achieves its long-range magnetic order of alternating up and down electron spins.

Physicists create first metamaterial with rewritable magnetic ordering
University of Notre Dame physicists and their collaborators have produced the first rewriteable artificial magnetic charge ice.

A quasiparticle collider
In the early 1900s, Ernest Rutherford shot alpha particles onto gold foils and concluded from their scattering properties that atoms contain their mass in a very small nucleus.

Impossible superconductors gone live
The scientists from the Faculty of Physics of the Lomonosov Moscow State University conducted a study evaluating the appearance of the superconducting state in the iron-based superconductors with two energetic gaps.

Insulator-superconductor transition of copper-oxide compound studied in fine detail
Using a highly controlled deposition technique, scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have synthesized ultrathin films containing multiple samples of a copper-oxide compound to study the compound's electronic behavior at near absolute zero, or minus 459 degrees Fahrenheit.

Scientists create laser-activated superconductor
Shining lasers at superconductors can make them work at higher temperatures, suggests new findings from an international team of scientists including the University of Bath.

Phosphine as a superconductor? Sure, but the story may be complicated
Phosphine is one of the newest materials to be named a superconductor, a material through which electricity can flow with zero resistance.

Cornell researchers create first self-assembled superconductor
Building on nearly two decades' worth of research, a multidisciplinary team at Cornell has blazed a new trail by creating a self-assembled, three-dimensional gyroidal superconductor.

Clarifying the role of magnetism in high-temperature superconductors
A collaboration of scientists from the RIKEN SPring-8 Center, Osaka University, the Japan Atomic Energy Agency, and the Japan Synchrotron Radiation Research Institute have published research clarifying the role of magnetism in a new type of high-temperature superconductor.

The route to high temperature superconductivity goes through the flat land
Superconductors are marvellous materials that are able to transport electric current and energy without dissipation.
More Superconductors Current Events and Superconductors News Articles

The Oxford Handbook of Small Superconductors (Oxford Handbooks)

The Oxford Handbook of Small Superconductors (Oxford Handbooks)
by A.V. Narlikar (Editor)

This handbook is about a remarkable set of materials that are technically referred to as "mesoscopic superconductors", which for all practical purposes are tiny or small in their dimensions, ranging from a few micrometers down to a nanometer. At this level of smallness, the superconducting properties are dramatically changed, showing the dominance of quantum effects. Ground breaking research studies of small superconductors have emerged, and in a world obsessed with miniaturization of electronic device technology, small superconductors acquire even greater relevance and timeliness for the development of exciting novel quantum devices.

The chapters, contributed by noted researchers and frontrunners in the field from 15 countries, are presented in three parts, namely progress in...

Introduction to Superconductivity: Second Edition (Dover Books on Physics) (Vol i)

Introduction to Superconductivity: Second Edition (Dover Books on Physics) (Vol i)
by Michael Tinkham (Author)

Well known for its accessibility to graduate students and experimental physicists, this volume emphasizes physical arguments and minimizes theoretical formalism. The second edition of this classic text features revisions by the author that improve its user-friendly qualities, and an introductory survey of latter-day developments in classic superconductivity enhances the volume’s value as a reference for researchers. Starting with a historical overview, the text proceeds with an introduction to the electrodynamics of superconductors and presents expositions of the Bardeen-Cooper-Schrieffer theory and the Ginzburg-Landau theory. Additional subjects include magnetic properties of classic type II superconductors; the Josephson effect (both in terms of basic phenomena and applications and of...

Plastic Fantastic: How the Biggest Fraud in Physics Shook the Scientific World (MacSci)

Plastic Fantastic: How the Biggest Fraud in Physics Shook the Scientific World (MacSci)
by Eugenie Samuel Reich (Author)

This is the story of wunderkind physicist Jan Hendrik Schön who faked the discovery of a new superconductor made from plastic. A star researcher at the world-renowned Bell Laboratories in New Jersey, he claimed to have stumbled across a powerful method for making carbon-based crystals into transistors, the switches found on computer chips. Had his experiments worked, they would have paved the way for huge advances in technology--computer chips that we could stick on a dress or eyewear, or even use to make electronic screens as thin and easy-to-fold as sheets of paper. But as other researchers tried to recreate Schön's experiments, the scientific community learned that it had been duped. Why did so many top experts, including Nobel prize-winners, support Schön? What led the major...

The 2018-2023 World Outlook for Superconductors

The 2018-2023 World Outlook for Superconductors
by Icon Group International (Author)

This study covers the world outlook for superconductors across more than 190 countries. For each year reported, estimates are given for the latent demand, or potential industry earnings (P.I.E.), for the country in question (in millions of U.S. dollars), the percent share the country is of the region, and of the globe. These comparative benchmarks allow the reader to quickly gauge a country vis-à-vis others. Using econometric models which project fundamental economic dynamics within each country and across countries, latent demand estimates are created. This report does not discuss the specific players in the market serving the latent demand, nor specific details at the product level. The study also does not consider short-term cyclicalities that might affect realized sales. The study,...

Superconductivity: A Very Short Introduction

Superconductivity: A Very Short Introduction
by Stephen J. Blundell (Author)

Superconductivity--the flow of electric current without resistance in certain materials as temperatures near absolute zero--is one of the greatest discoveries of 20th century physics, but it can seem impenetrable to those who lack a solid scientific background. Outlining the fascinating history of how superconductivity was discovered, and the race to understand its many mysterious and counter-intuitive phenomena, Stephen Blundell explains in accessible terms the theories that have been developed to explain it, and how they have influenced other areas of science, including the Higgs boson of particle physics and ideas about the early Universe. This Very Short Introduction examines the many strange phenomena observed in superconducting materials, the latest developments in high-temperature...

Topological Insulators and Topological Superconductors

Topological Insulators and Topological Superconductors
by B. Andrei Bernevig (Author), Taylor L. Hughes (Contributor)

This graduate-level textbook is the first pedagogical synthesis of the field of topological insulators and superconductors, one of the most exciting areas of research in condensed matter physics. Presenting the latest developments, while providing all the calculations necessary for a self-contained and complete description of the discipline, it is ideal for graduate students and researchers preparing to work in this area, and it will be an essential reference both within and outside the classroom. The book begins with simple concepts such as Berry phases, Dirac fermions, Hall conductance and its link to topology, and the Hofstadter problem of lattice electrons in a magnetic field. It moves on to explain topological phases of matter such as Chern insulators, two- and three-dimensional...

The Theory of Superconductivity in the High-Tc Cuprate Superconductors

The Theory of Superconductivity in the High-Tc Cuprate Superconductors
by P. W. Anderson (Author)

This book is P. W. Anderson's long-awaited full presentation of his theory of high-T"c" superconductivity in the cuprates. He realized that this striking new phenomenon needed for its explanation not just a new mechanism or "gimmick" but a radical reworking of the electronic theory of metals, especially those of low dimension. The many fundamentally new ideas that are first fully presented here will require a rewriting of the textbooks of many-body theory, which may take decades. The book incorporates full discussions of the experimental situation in these complex materials, both the normal and the superconducting states. The latest advances are contained in a selection of re-and pre-prints of recent work by Anderson and collaborators.
The fundamental insight contained in...

Ugly's Electrical References, 2014 Edition

Ugly's Electrical References, 2014 Edition
by Jones & Bartlett Learning (Author)

Ugly's Electrical References, 2014 Edition is designed to be used as an on-the-job reference. Used worldwide by electricians, engineers, contractors, designers, maintenance workers, instructors, and the military; Ugly's contains the most commonly required electrical information in an easy-to-read and easy-to-access format. Ugly's presents a succinct portrait of the most pertinent information all electricians need at their fingertips, including: mathematical formulas, National Electrical Code tables, wiring configurations, conduit bending, voltage drops, and life-saving first aid procedures.

Barron's 500 Flash Cards of American Sign Language

Barron's 500 Flash Cards of American Sign Language
by Geoffrey S. Poor (Author)

Full-color photos on flash cards present close-ups of a model demonstrating 500 American Sign Language (ASL) signs. The meanings, brief descriptions of hand and arm motions, and related words are listed on the reverse side of each card. Correct formations of hand shapes and facial expressions are clearly shown to eliminate any possible confusion regarding intended word meanings. Where appropriate, photos include directional arrows that show hand or arm movements. Each flash card has a hole in one corner to accommodate a metal ring included with the boxed set. Users can select and fit any combination of cards they please to combine relevant words and create statements, or to review signs that they have difficulty identifying. Here is an ideal method for recognizing and memorizing American...

Experimental Techniques: Cryostat Design, Material Properties and Superconductor Critical-Current Testing

Experimental Techniques: Cryostat Design, Material Properties and Superconductor Critical-Current Testing
by Jack Ekin (Author)

This book presents a highly integrated, step-by-step approach to the design and construction of low-temperature measurement apparatus. It is effectively two books in one: A textbook on cryostat design techniques and an appendix data handbook that provides materials-property data for carrying out that design. The main text encompasses a wide range of information, written for specialists, without leaving beginning students behind. After summarizing cooling methods, Part I provides core information in an accessible style on techniques for cryostat design and fabrication - including heat-transfer design, selection of materials, construction, wiring, and thermometry, accompanied by many graphs, data, and clear examples. Part II gives a practical user's perspective of sample mounting...

© 2017