Science Current Events | Science News | Brightsurf.com
 

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 (http://www.bnl.gov/energy/ces/) 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

Growth and Characterization of Bulk Superconductor Material (Springer Series in Materials Science)

Growth and Characterization of Bulk Superconductor Material (Springer Series in Materials Science)
by Dapeng Chen (Author), Chengtian Lin (Author), Andrey Maljuk (Author), Fang Zhou (Author)


This book focuses on recently developed crystal growth techniques to grow large and high quality superconducting single crystals. The techniques applied are traveling solvent floating zone (TSFZ) with infrared image furnace, Bridgeman, solution/flux and top seeded solution growth (TSSG) methods. The materials range from cuprates, cobaltates to pnictides including La2CuO4-based (LCO), YBa2Cu3O7-d (YBCO), Bi2Sr2Can-1CunO2n+4+δ (n=1,2,3) (BSCCO) to NaxCoO2. The modified Bridgman “cold finger” method is devoted to the pnictide system with the best quality (transition width DTc~0.5 K) with highest Tc~38.5 K of Ba0.68K0.32Fe2A2. The book presents various iron-based superconductors with different structures, such as 1111, 122, 111, 11 and 42622,10-3-8. Detailed single crystal growth methods...

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...

Superconductors

Superconductors
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....

Superconductors in the Power Grid: Materials and Applications (Woodhead Publishing Series in Energy)

Superconductors in the Power Grid: Materials and Applications (Woodhead Publishing Series in Energy)
by C. Rey (Editor)


Superconductors offer high throughput with low electric losses and have the potential to transform the electric power grid. Transmission networks incorporating cables of this type could, for example, deliver more power and enable substantial energy savings. Superconductors in the Power Grid: Materials and Applications provides an overview of superconductors and their applications in power grids. Sections address the design and engineering of cable systems and fault current limiters and other emerging applications for superconductors in the power grid, as well as case studies of industrial applications of superconductors in the power grid.Expert editor from highly respected US government-funded research centreUnique focus on superconductors in the power gridComprehensive...

Superconductors

Superconductors
by Christopher Lampton (Author)


Discusses the science, history, and potential applications of this exciting scientific breakthrough.

The Physics of Organic Superconductors and Conductors (Springer Series in Materials Science)

The Physics of Organic Superconductors and Conductors (Springer Series in Materials Science)
by Andrei Lebed (Editor)


This bang up-to-date volume contains the distilled wisdom of some of the world’s leading minds on the subject. Inside, there is a treasure trove of general (tutorial) and topical reviews, written by leading researchers in the area of organic superconductors and conductors. The papers hail from all over the world, as far afield as the USA and Australia. They cover contemporary topics such as unconventional superconductivity, non-Fermi-liquid properties, and the quantum Hall effect.

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...

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...

Organic Superconductors (Springer Series in Solid-State Sciences)

Organic Superconductors (Springer Series in Solid-State Sciences)
by Takehiko Ishiguro (Author), Kunihiko Yamaji (Author), Gunzi Saito (Author)


Organic Superconductors is an introduction to organic conductors and superconductors and a review of the current status of the field. First, organic conductors are described, then the structures and electronic properties of organic superconductors are discussed, illustrated with examples of typical compounds. The book deals in detail with theories of the mechanism of superconductivity, and more briefly with spin-density waves. The design, principle, and synthesis of organic superconductors are also described. This second edition covers the research activities of the last few years.

Non-Centrosymmetric Superconductors: Introduction and Overview (Lecture Notes in Physics)

Non-Centrosymmetric Superconductors: Introduction and Overview (Lecture Notes in Physics)
by Ernst Bauer (Editor), Manfred Sigrist (Editor)


Superconductivity in materials without inversion symmetry in the respective crystal structures occurs in the presence of antisymmetric spin-orbit coupling as a consequence of an emerging electric field gradient. The superconducting condensate is then a superposition of spin-singlet and spin-triplet Cooper pairs. This scenario accounts for various experimental findings such as nodes in the superconducting gap or extremely large upper critical magnetic fields. Spin-triplet pairing can occur in non-centrosymmetric superconductors in spite of Anderson's theorem that spin-triplet pairing requires a crystal structure that exhibits inversion symmetry. This book, authored and edited by leading researchers in the field, is both an introduction to and overview on this exciting branch of novel...

© 2016 BrightSurf.com