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

Titania-Based Material Holds Promise as New Insulator for Superconductors
Research from North Carolina State University shows that a type of modified titania, or titanium dioxide, holds promise as an electrical insulator for superconducting magnets, allowing heat to dissipate while preserving the electrical paths along which current flows.

Refocusing research into high-temperature superconductors
Below a specific transition temperature superconductors transmit electrical current nearly loss-free. For the best of the so-called high-temperature superconductors, this temperature lies around -180 °C - a temperature that can be achieved by cooling with liquid nitrogen.

Study finds physical link to strange electronic behavior
Scientists have new clues this week about one of the baffling electronic properties of the iron-based high-temperature superconductor barium iron nickel arsenide.

Physicists unlock nature of high-temperature superconductivity
Physicists have identified the "quantum glue" that underlies a promising type of superconductivity -- a crucial step towards the creation of energy superhighways that conduct electricity without current loss.

Magnets for fusion energy: A revolutionary manufacturing method developed
The National Institute for Fusion Science (NIFS), of the National Institutes of Natural Sciences (NINS) in Japan, has achieved an electrical current of 100,000 amperes, which is by far the highest in the world, by using the new idea of assembling the state-of-the-art yttrium-based high-temperature superconducting tapes to fabricate a large-scale magnet conductor.

Superconductivity could form at high temperatures in layered 2D crystals
An elusive state of matter called superconductivity could be realized in stacks of sheetlike crystals just a few atoms thick, a trio of physicists has determined.

Study helps unlock mystery of high-temp superconductors
A Binghamton University physicist and his colleagues say they have unlocked one key mystery surrounding high-temperature superconductivity.

Quantum criticality observed in new class of materials
Quantum criticality, the strange electronic state that may be intimately related to high-temperature superconductivity, is notoriously difficult to study. But a new discovery of "quantum critical points" could allow physicists to develop a classification scheme for quantum criticality - the first step toward a broader explanation.

X-ray pulses on demand from electron storage rings
Everything we know nowadays about novel materials and the underlying processes in them we also know thanks to studies at contemporary synchrotron facilities like BESSY II.

NCNR neutrons highlight possible battery candidate
Analysis of a manganese-based crystal by scientists at the National Institute of Standards and Technology (NIST) and the Massachusetts Institute of Technology (MIT) has produced the first clear picture of its molecular structure.
More Superconductors Current Events and Superconductors News Articles

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), Physics (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...

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...


by A. V. Narlikar (Author)

Superconductors is neither about basic aspects of superconductivity nor about its applications, but its mainstay is superconducting materials. Unusual and unconventional features of a large variety of novel superconductors are presented and their technological potential as practical superconductors assessed. The book begins with an introduction to basic aspects of superconductivity. The presentation is readily accessible to readers from a diverse range of scientific and technical disciplines, such as metallurgy, materials science, materials engineering, electronic and device engineering, and chemistry. The derivation of mathematical formulas and equations has been kept to a minimum and, wherever necessary, short appendices with essential mathematics have been added at the end of the text....

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...

Carbon-based Superconductors: Towards High-Tc Superconductivity

Carbon-based Superconductors: Towards High-Tc Superconductivity
by Junji Haruyama (Editor)

This book describes basic physics and the recent advancement of carbon-based superconductors (CBSCs), such as diamond, graphite, graphene, carbon nanotubes (CNTs), and others. The small mass of carbon atoms provides high phonon frequency, high Debye temperature, and chances to high superconducting transition temperature (Tc). Individual materials also provide different mechanisms and chances to high Tc. Consequently, it is highly expected that CBSCs will open the door to high-Tc superconductivity, for example, CuO2-based SCs.

  New Superconductors: From Granular To High Tc: Second Edition
by Guy Deutscher (Author)

How new are the high Tc superconductors, as compared to the conventional low Tc ones? In what sense are these oxides different from regular metals in their normal state? How different is the mechanism for high Tc superconductivity from the well-known electron-phonon interaction that explains so well superconductivity in metals and alloys? What are the implications of the new features of the high Tc oxides for their practical applications? This interesting book aims to provide some answers to those questions, drawing particularly on similarities between the high Tc oxides and granular superconductors, which also present a short coherence length, a small superfluid density and an inhomogeneous structure.

The Physics of Superconductors: Vol. I. Conventional and High-Tc Superconductors

The Physics of Superconductors: Vol. I. Conventional and High-Tc Superconductors
by Karl-Heinz Bennemann (Editor), John B. Ketterson (Editor)

This is the first volume of a comprehensive two-volume treatise on superconductivity that represents the first such publication since the earlier work by R. Parks. It systematically reviews the basic physics and recent advances in the field. Leading researchers describe the state of the art in conventional phonon-induced superconductivity, high-Tc superconductivity, and novel superconductivity. After an introduction and historical overview, the leaders in the special fields of research give a comprehensive survey of the basics and the state of the art in chapters covering the entire field of superconductivity, including conventional and unconventional superconductors. Important new results are reported in a manner intended to stimulate further research. Numerous illustrations, diagrams...

Flux Pinning in Superconductors (Springer Series in Solid-State Sciences)

Flux Pinning in Superconductors (Springer Series in Solid-State Sciences)
by Teruo Matsushita (Author)

The book covers the flux pinning mechanisms and properties and the electromagnetic phenomena caused by the flux pinning common for metallic, high-Tc and MgB2 superconductors. The condensation energy interaction known for normal precipitates or grain boundaries and the kinetic energy interaction proposed for artificial Nb pins in Nb-Ti, etc. are introduced for the pinning mechanism. Summation theories to derive the critical current density are discussed in detail. Irreversible magnetization and AC loss caused by the flux pinning are also discussed. The loss originally stems from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the flux motion.The readers will learn why the resultant loss is of hysteresis type in spite of such mechanism....

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...

Electrodynamic Theory of Superconductors (Ieee Electromagnetic Waves Series)

Electrodynamic Theory of Superconductors (Ieee Electromagnetic Waves Series)
by S.A. Zhou (Author)

This book presents a unified and comprehensive theoretical treatment of electromagnetic, thermal and mechanical phenomena in superconductors. Introduces basic concepts and principles with particular emphasis on general methodology.

© 2014