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

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....

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...

Superconductors

Superconductors
by Christopher Lampton (Author)


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

High Temperature Superconductors

High Temperature Superconductors
by Raghu N. Bhattacharya (Editor), M. Parans Paranthaman (Editor)


This essential reference provides the most comprehensive presentation of state-of-the-art research being conducting worldwide today in this growing field of research and applications. HTS are currently being supported by numerous governmental and industrial initiatives in the USA and Asia and Europe to overcome energy distribution issues and are now being commercialised for power-delivery devices, such as power transmission lines and cables, motors, and generators. Applications in electric utilities include energy-storing devices to help industries avoid dips in electric power, current limiters, and long transmission lines. The technology is particularly thought out for highly-populated and densed areas.

Both editors are leading experts in the field from the National Renewable...

Layered Superconductors: Volume 1 (International Series of Monographs on Physics)

Layered Superconductors: Volume 1 (International Series of Monographs on Physics)
by Richard A. Klemm (Author)


Since the discovery by the author and collaborators of superconductivity in the first truly layered compound, TaS2(pyridine)1/2, there have been many types of layered superconductors. These include the graphite intercalation compounds, the transition metal dichalcogenides, the intercalated transition metal dichalcogenides, the organic layered superconductors, the high-temperature cuprates, the various types of artificial multilayers, strontium ruthenate, magnesium diboride, the ternary intermetallics, the quaternary intermetallics or borocarbides, the iron pnictides and oxypnictides, the iron chalcogenides, and the intercalated metal nitride halides. In the development of this huge field, an underlying theme has always been to try to develop a room-temperature superconductor. Since...

Chemistry of Superconductor Materials: Preparation, Chemistry, Characterization, and Theory (Materials Science and Process Technology Series)

Chemistry of Superconductor Materials: Preparation, Chemistry, Characterization, and Theory (Materials Science and Process Technology Series)
by Terrell A. Vanderah (Author)


This thorough review of the chemistry of high Tc superconductors provides extensive coverage of the structural and synthetic solid-state chemistry of oxide superconductors as well as substantial reference material on characterization methods. Written by 27 authorities in the field, the book fulfills a need for a condensed, single-source reference. It will be indispensable for researchers and for those unfamiliar with structural and synthetic solid-state chemistry of superconductors.

Conductors, Semiconductors, Superconductors: An Introduction to Solid State Physics (Undergraduate Lecture Notes in Physics)

Conductors, Semiconductors, Superconductors: An Introduction to Solid State Physics (Undergraduate Lecture Notes in Physics)
by Rudolf P. Huebener (Author)


In the second half of the last century solid state physics and materials science experienced a great advance and established itself as an important and independent new field.This book provides an introduction to the fundamentals of solid state physics, including a description of the key people in the field and the historic context. The book concentrates on the electric and magnetic properties of materials. It is written for students up to the bachelor in the fields of physics, materials science and electric engineering. Because of its vivid explanations and its didactic approach, it can also serve as a motivating pre-stage and supporting companion in the study of the established and more detailed textbooks of solid state physics. The book is suitable for a quick repetition prior to...

Superconductors: Conquering Technology's New Frontier

Superconductors: Conquering Technology's New Frontier
by Randy Simon (Author), Andrew Smith (Author)




High-Temperature-Superconductor Thin Films at Microwave Frequencies (Springer Tracts in Modern Physics)

High-Temperature-Superconductor Thin Films at Microwave Frequencies (Springer Tracts in Modern Physics)
by Matthias Hein (Author)


The book develops a comprehensive understanding of the surface impedance of the oxide high-temperature superconductors in comparison with the conventional superconductor Nb3Sn. Linear and nonlinear microwave responses are treated separately, both in terms of models, theories or numerical approaches and in terms of experimental results. The theoretical treatment connects fundamental aspects of superconductivity to the specific high-frequency properties. The experimental data review the state of the art, as reported by many international groups. The book describes further the main features of appropriate preparation, handling, mounting, and refrigeration techniques, and finally discusses possible applications in passive and active microwave devices.

© 2016 BrightSurf.com