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 materials design related to superconductivity and the creation of more efficient semiconductors for various electronic device applications.
The study is published in Scientists progressa peer-reviewed multidisciplinary scientific journal published by the American Association for the Advancement of Science.
Strontium titanate has been on the radar of scientists for 60 years because it exhibits many interesting properties. On the one hand, it becomes a superconductor, that is, it conducts electricity smoothly without resistance, at low temperature and with low concentration of electrons. It also undergoes a structural change at 110 Kelvin (-262 degrees Fahrenheit), which means that the atoms in its crystal structure change their 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 led by 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 the structural change within strontium titanate directly affects how electric current flows through the material. They also revealed how small changes in the concentrations of electrons in the material affect its superconductivity. This knowledge will ultimately inform future research on this material, including research into 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 make new devices and technologies,” said Bharat Jalan, lead author and associate professor and Shell Professor at the University of Minnesota Twin Cities Department of Chemical Engineering and Materials Science. “What this study shows is a link between 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 the fact that they were able to synthesize an extremely “clean” strontium titanate material, i.e. it contained very little 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 macroscopic properties observed experimentally to the microscopic behavior of electrons.
“The observed response of superconducting properties to small changes in electron density provides new pieces in the ongoing puzzle of superconductivity in strontium titanate,” said the professor of physics and astronomy at the University of Minnesota and contributing author Rafael Fernandes, whose group managed the theoretical 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 materials synthesis and transport measurements; Fernandes, whose group performed the theoretical calculations; and Vlad Pribiag, associate professor in the School of Physics and Astronomy, specializing in advanced measurement of thin film properties.
“Many questions in modern science and engineering are so complex that they transcend a single discipline,” Pribiag said. “Having these collaborations available within the same college is extremely useful. You need all of 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 (student at doctorate), Dooyong Lee (associate postdoctoral fellow), and Laxman Thoutam (postdoctoral fellow); University of Minnesota School of Physics and Astronomy researchers Yilikal Ayino (Ph.D. ’21) and Maria Gastiasoro (postdoctoral associate); and Bar-Ilan University Physics Department researchers Beena Kalisky (professor), Eylon Persky (PhD student) and Alex Khanukov (PhD student).
This research was supported by the U.S. Department of Energy through the Center for Quantum Materials at the University of Minnesota, Air Force Office of Scientific Research, National Science Foundation Materials Science and Engineering Research Center from the University of Minnesota, the Israel Science Foundation and the QuantERA ERA-NET co-fund in quantum technologies.