September 8, 2022 – In collaboration with a team of researchers from Africa and the United States, Garu Gebreyesus, Lecturer in Physics at the University of Ghana, recently used Expanse at the San Diego Supercomputer Center at UC San Diego to examine the electronic structure and magnetism of strontium ruthenates, a class of layered materials with diverse properties.
The international team’s study was recently published in the American Physical Society’s Journal Physical Review B and explained Gebreyesus’ theoretical prediction: the three-layer material, ruthenate, is almost “half metallic”, a metal in which all the electrons spin in one direction. The article goes on to explain that small applied magnetic fields could tip the scales and create giant magneto-electric effects. This may be important for “spintronics” which has quickly become a field of study within the physics community due to the possibility of using this concept to create new low-power electronic devices.
“While magnetism and superconductivity are two of the most important properties of materials, some magnetic materials are much better than iron for electric motors,” Gebreyesus explained. “They are the reason why small motors can power electric bicycles and scooters while larger such motors make efficient electric cars.”
“The ruthenate material is a magnet whose properties can be changed by applying magnetic fields, which are potentially useful for electronic circuits and memory elements,” he continued. “Our theoretical work has made predictions that explain the experimental data and provided a new interpretation different from previous work – the key point is the effect of magnetism, and now we are conducting experiments to test our predictions.”
Gebreyesus worked closely with co-author Prosper Ngabonziza, an experimenter from Rwanda who conducted some of the paper’s experiments in South Africa prior to runs on Expanse. Through workshops offered by the African School of Electronic Structure Methods and Applications (ASESMA), Gebreyesus and Ngabonziza were introduced to longtime supercomputer user Richard Martin, a professor of physics at Stanford University and the University of Illinois, who suggested running their theoretical calculations on Scope for faster turnaround time.
“It was great introducing Expanse to Garu and Prosper,” Martin said. “ASESMA brings together researchers from Africa with researchers from the United States and Europe so that excellent research can be carried out if computing facilities are available. We were excited to secure the grants on Expanse not only to advance this work, but also to connect our African colleagues with researchers doing similar work in the United States.
After the publication of their paper, Gebreyesus and Ngabonziza were noticed by American researchers conducting similar work and are now partnering remotely with Jonathan Denlinger and Alexei Fedorov at the Lawrence Berkeley National Laboratory (LBNL) to further test the predictions published in their article. Gebreyesus recently visited LBNL to give a talk about their work and meet Denlinger and Fedorov in person.
“I was excited to travel to LBNL and explore new experiences about our work and related issues,” Gebreyesus said. “My LBNL time was funded by the United States-Africa Electronic Structure Initiative (USAfrI) – through initiatives like this and time spent on Expanse, we are able to conduct our research that will enable a more efficient low-power electronics day.”
Funding for the supercomputing performed on Expanse was provided by National Science Foundation Extreme Science and Engineering Discovery Environment (XSEDE) award number TG-PHY210045.
*Image: Strontium ruthenates form crystals with layered metallic materials of ruthenium-oxygen spaced apart by insulating layers of strontium oxide. They have been of great interest in understanding why single atomic layers of ruthenium separated by layers of strontium become an unconventional superconductor; a double layer has a phase transition with an applied magnetic field; and a triple layer becomes a ferromagnet like iron, but with different behavior parallel and perpendicular to the planes. Single and dual systems have been widely studied, but only recently have experiments been reported on the nature of the electronic states on the triple-layered material.
Source: Kimberly Mann Bruch, SDSC External Relations