A team led by researchers from the University of Minnesota Twin Cities has discovered how subtle structural changes in strontium titanate, a metal oxide semiconductor, can alter the material’s electrical resistance and affect its superconducting properties.
The research can help guide future experiments and material design related to superconductivity and the creation of more efficient semiconductors for various electronic device applications.
The study was published in Scientists are progressinga multidisciplinary, peer-reviewed scientific journal published by the American Association for the Advancement of Science.
Strontium titanate has been on scientists’ radar for 60 years because of its many interesting properties. On the one hand, it becomes a superconductor, that is, it conducts electricity smoothly, without resistance, at low temperature and with a small concentration of electrons. It also undergoes a structural change at 110 Kelvin (-262 degrees Fahrenheit), meaning the atoms in its crystal structure change arrangement. However, scientists are still debating what exactly causes superconductivity in this material at the microscopic level, or what happens when its structure changes.
In this study, the team around the University of Minnesota was able to shed light on these questions.
Using a combination of materials synthesis, analysis and theoretical modelling, the researchers found that structural change within strontium titanate directly affects how electric current flows through the material. They also showed how small changes in electron concentration in the material affect its superconductivity. This knowledge will ultimately inform future research on this material, including exploration of its unique superconducting properties.
“The backbone of human life relies on the discovery of new properties in materials, and scientists and engineers can use these properties to create new devices and technologies,” said Bharat Jalan, lead author and associate professor and Shell Professor at the University of Minnesota Twin City Department of Chemical Engineering and Materials Science. “What this study shows is a connection between the superconductivity and the material structure of strontium titanate. But perhaps more importantly, it shows that a collaborative approach is essential to solving complex problems in science and engineering. »
One of the main reasons the researchers were able to make this discovery was that they were able to synthesize an extremely ‘clean’ strontium titanate material, meaning it contained very few impurities. To do this, they used a technique called Hybrid Molecular Beam Epitaxy (MBE) – an approach pioneered by Jalan’s lab.
Because the material was so clean, the researchers were able to make unprecedented observations in strontium titanate. Thanks to theoretical modelling, the researchers were able to relate the experimentally observed macroscopic properties to the microscopic behavior of electrons.
“The observed response of the superconducting properties to small changes in electron density provides new pieces in the ongoing puzzle of superconductivity in strontium titanate,” said University of Minnesota professor of physics and astronomy and contributing author Rafael Fernandes, whose group led the theory modeling aspect of the research .
This research was made possible through a collaboration between three faculty members from the University of Minnesota’s Twin Cities: Jalan, whose lab led the effort and managed the material synthesis and transport measurements; Fernandes, whose group carried out the theoretical calculations; and Vlad Pribiag, associate professor at the Faculty of Physics and Astronomy, specializing in advanced measurement of thin film properties.
“Many questions in modern science and technology are so complex that they transcend a single discipline,” said Pribiag. “Having these collaborations available within the same university is extremely useful. You need all these ingredients to solve many problems. »
In addition to Jalan, Fernandes, and Pribiag, the research team included researchers from the Department of Chemical Engineering and Materials Science at the University of Minnesota, Jin Yue (Ph.D. ’21), Tristan Truttmann (PhD student), Dooyong Lee (associate postdoctoral fellow), and Laxman Thoutam ( postdoc); University of Minnesota School of Physics and Astronomy researchers, Yilikal Ayino (Ph.D. ’21) and Maria Gastiasoro (postdoctoral researcher); and researchers from the Physics Department of Bar-Ilan University Beena Kalisky (professor), Eylon Persky (PhD student) and Alex Khanukov (PhD student).
This research was funded by the US Department of Energy through the Center for Quantum Materials at the University of Minnesota, the Air Force Office of Scientific Research, the National Science Foundation Materials Science and Engineering Research Center at the University of Minnesota, the Israel Science Foundation, and the QuantERA ERA -NET co-funding in quantum technologies.
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