Rutgers team develops computational model for predicting superconductivity
Researchers studying iron-based superconductors are combining novel electronic structure algorithms with the high-performance computing power of the Department of Energy’s Titan supercomputer at Oak Ridge National Laboratory to predict spin dynamics, or the ways electrons orient and correlate their spins in a material. Because researchers have suggested that spin dynamics create the conditions needed for superconductivity, this approach could expedite the search for new or modified materials that conduct electricity with little or no resistance at higher temperatures, unlike current commercial superconductors, which must be expensively cooled to exhibit superconducting properties.
The 15 boxes in this image show the simulated intensity of spin excitations in 15 iron-based materials, including iron compounds that are high-temperature superconductors (images d–h). The x axis shows the momentum of the spin excitation in selected locations of 3D space, and the y axis shows the energy measured in electron volts (eV). The color code indicates the intensity of spin excitations with a given energy and momentum, which is compared with available experimental results (shown in black bars in images f, g, l, and m). The locations with the greatest number of spin excitations are shown in red with decreasing frequency shown from orange to blue. By visualizing the spin dynamics of multiple iron-based materials—information that can be time-consuming and expensive to collect experimentally—researchers can better predict which materials are likely to be superconducting.
In a Nature Physics paper published in October, Zhiping Yin, Kristjan Haule, and Gabriel Kotliar of Rutgers University compute the dynamic spin structure factors—or the measure of how the spins of electrons align relative to each other at a given distance at different times—of 15 iron-based materials, including several high-temperature superconductors, in unprecedented detail.
“Our computational results are in good agreement with experimental results for experiments that have been performed, and we have several predictions for compounds that have not yet been measured,” Kotliar said. “Once we validate the theory that our computational models are based on with experiments, then we can investigate materials computationally that are not being studied experimentally.”
Computation offers a way for researchers to better understand spin dynamics and other material properties under many conditions, such as temperature change, rather than the singular condition present during a given experiment. Computation also allows researchers to simulate many of these materials at once, and the number of potential materials to explore rapidly increases as scientists introduce modifications to improve performance.
With the computational power at hand on the 27-petaflop Titan system managed by the Oak Ridge Leadership Computing Facility, the team was able to compare and contrast spin dynamics for all 15 materials simulated to identify tell-tale superconducting properties.
“By comparing simulations and experiments, we learned about which type of spin fluctuations actually promote superconductivity and which ones do not,” Kotliar said.
In their model, the team used a technique called Dynamical Mean Field Theory to reduce the vast number of interactions involving electrons in a unit cell (the most detailed slice of material simulated) and averaged these interactions in a mean field environment across the rest of the solid. The team used the Monte Carlo method to statistically select the best solutions for these techniques, achieving a new level of predictive accuracy for spin dynamics in these kinds of materials.
“We find these complex problems, as in superconductors, where you have to solve many degrees of freedom or a large number of variables, require supercomputing rather than computing on smaller clusters,” Haule said. “Our algorithms are designed to work very efficiently on Titan’s massively parallel architecture.”
Using 20 million processor-hours on Titan, the team also discovered through simulation a new superconducting state, or electron pairing, found in the lithium-iron-arsenic compound, LiFeAs, that is consistent with experimental results.
In the future, they plan to simulate spin dynamics in other classes of superconductors and in non-superconducting materials that are exceptionally difficult to study experimentally, such as radioactive materials.
“Using computation as a substitute for experiment is an important step forward for designing new materials,” Kotliar said. “The next time someone comes to us with potential materials for an application and asks, ‘Should I work on this?’ we hope to simulate that material through computation to select the most promising ones.”
The work was supported by the National Science Foundation and made use of the Oak Ridge Leadership Computing Facility, a DOE Office of Science User Facility at ORNL.
UT-Battelle manages ORNL for the Department of Energy's Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.
For more information, please visit http://science.energy.gov/
Katie Elyce Jones
Katie Jones | newswise
Research finds new molecular structures in boron-based nanoclusters
13.07.2018 | Brown University
3D-Printing: Support structures to prevent vibrations in post-processing of thin-walled parts
12.07.2018 | Fraunhofer-Institut für Produktionstechnologie IPT
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
13.07.2018 | Event News
13.07.2018 | Materials Sciences
13.07.2018 | Life Sciences