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
New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University
Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology