New Instrument Puts New Spin on SuperconductorsOctober 13, 2008Ames Lab researchers team up to probe iron-arsenic superconductors AMES, Iowa -Researchers at the U.S. Department of Energy's Ames Laboratory are part of collaborative team that's used a brand new instrument at the DOE's Spallation Neutron Source to probe iron-arsenic compounds, the "hottest" new find in the race to explain and develop superconducting materials. Rob McQueeney, an Ames Laboratory physicist, was part of that team whose findings, published in the Oct. 8 issue of Physical Review Letters, mark the first research produced with the aid of the new tool. The Spallation Neutron Source - SNS for short - is the DOE's sprawling new $1.4 billion complex operated by Oak Ridge National Laboratory in the rolling green hills of eastern Tennessee. The SNS uses a pulsed neutron beam to provide information about the structure and dynamics of materials that cannot be obtained from X-rays or electron microscopes. Although neutral in electrical charge, neutrons interact with the nucleus. The neutron's magnetic moment can also interact with magnetic spins in a material. As neutrons from the beam pass through a material, they scatter off the nuclei and spins. By measuring the speed and angle of the scattered neutrons, scientists are able to develop detailed information about the positions and the motion of the nuclei and spins within the material. McQueeney serves on the Executive Committee of the Instrumentation Development Team for ARCS, a wide angular-range chopper spectrometer designed to measure the vibrations of atomic nuclei. The sixth of the proposed 24 instruments to be built at the SNS, ARCS is undergoing final testing and is available for general use this fall, but McQueeney is already impressed with the results. "The preliminary results are amazing," McQueeney said. "I have experience with a similar instrument and ARCS blew it away," adding that it produces better results from smaller samples in a much shorter time frame. The timing of the testing phase for ARCS was ideal because in the preceding months, a new class of superconducting materials - pnictide compounds based on iron and arsenic - was discovered. This allowed McQueeney and collaborators at Oak Ridge National Laboratory and California Institute of Technology to look specifically at lanthanum-iron-arsenide (LaFeAsO0.89F0.11). One of the samples studied was produced by McQueeney's Ames Laboratory colleague, physicist and crystal-growth expert Paul Canfield. When this new class of superconductors was first announced, Canfield was able to quickly replicate the results and develop additional compounds. The phenomenon of superconductivity is caused by the pairing of conduction electrons due to forces within the crystal. The origin of this pairing is one of the great unsolved mysteries in the field of high-temperature superconductivity. "There are two prevailing ideas behind superconductivity," McQueeney said. "One is that pairing is mediated by lattice vibrations. The other is that it's mediated by magnetic or spin fluctuations." Since neutrons are capable of measuring both the lattice vibrations and spin fluctuations, they are an ideal probe to gain an understanding of superconductivity. The experiments focused on understanding the role of lattice vibrations in the new superconductors. The vibration of atoms within the crystal lattice creates a pattern of waves called phonons. When a neutron collides with this lattice, it can give up some of its energy to create a phonon. The difference in the neutron's energy before and after the collision is equal to the phonon energy. "Our measurements did not support the conventional electron-phonon mediated superconductivity," McQueeney said, adding that theoretical calculations matched up fairly well with measurements obtained with ARCS. While the results are an important first step, there is still much work to be done to determine the origin of superconductivity in the iron-arsenides. McQueeney and his collaborators are continuing studies of phonons and spin excitations in these compounds. The quest to understand and develop superconductor technology has important energy implications. By their nature, and as the name implies, superconductors can conduct electrical current with virtually no power loss, unlike conventional electric transmission lines which lose up to 30% due to resistance in the system. Basic research to understand the atomic interactions that make superconductors work, and to potentially control those properties, is one way that Ames Laboratory strives to address the scientific challenges facing our country. Ames Laboratory is a U.S. Department of Energy Office of Science research facility operated by Iowa State University. Ames Laboratory creates innovative materials, technologies and energy solution. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global challenges. Ames Laboratory |
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| Related Superconductor Current Events and Superconductor News Articles 0.2 second test for explosive liquids Since a failed terrorist attack in 2006, plane passengers have not been able to carry bottles of liquid through security at airports, leaving some parched at the airport and others having expensive toiletries confiscated, but work by a group of physicists in Germany is paving the way to eliminate this necessary nuisance. For future superconductors, a little bit of lithium may do hydrogen a lot of good Scientists have a long and unsuccessful history of attempting to convert hydrogen to a metal by squeezing it under incredibly high and steady pressures. Scientists detect 'fingerprint' of high-temp superconductivity above transition temperature A team of U.S. and Japanese scientists has shown for the first time that the spectroscopic "fingerprint" of high-temperature superconductivity remains intact well above the super chilly temperatures at which these materials carry current with no resistance. On the path to metallic hydrogen Hydrogen, the most common element in the universe, is normally an insulating gas, but at high pressures it may turn into a superconductor. Superconductivity: Which one of these is not like the other? Superconductivity appears to rely on very different mechanisms in two varieties of iron-based superconductors. NIST discovers how strain at grain boundaries suppresses high-temperature superconductivity Researchers at the National Institute of Standards and Technology (NIST) have discovered that a reduction in mechanical strain at the boundaries of crystal grains can significantly improve the performance of high-temperature superconductors (HTS). Thinnest superconducting metal created A superconducting sheet of lead only two atoms thick, the thinnest superconducting metal layer ever created, has been developed by physicists at The University of Texas at Austin. New element found to be a superconductor Of the 92 naturally occurring elements, add another to the list of those that are superconductors. Iron-arsenic superconductors in class of their own Physicists at the U.S. Department of Energy's Ames Laboratory have experimentally demonstrated that the superconductivity mechanism in the recently-discovered iron-arsenide superconductors is unique compared to all other known classes of superconductors. Magnetism governs properties of iron-based superconductors Though a year has passed since the discovery of a new family of high-temperature superconductors, a viable explanation for the iron-based materials' unusual properties remains elusive. But a team of scientists working at the National Institute of Standards and Technology (NIST) may be close to the answer. More Superconductor Current Events and Superconductor News Articles |
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