VINSE Colloquium Series: “The Many Phases of AV3Sb5 Kagome Metals (A case study for first principles methods and group theory)” Dr. Turan Birol, University of Minnesota 1/25/23

Abstract. First principles computational methods, such as Density Functional Theory (DFT), provide a reliable means to both reproduce and predict the properties of crystalline materials. These approaches also allow performing thought experients to elucidate the microscopic mechanisms of macroscopic phenomena, and build structure-property relationships. DFT has been instrumental, for example, in understanding the physics of ferroelectricity. In this talk, I am going to present results from our ongoing work on the vanadium based Kagome metals with chemical formula AV3Sb5 (A=Cs, Rb, K). These materials undergo a series of crystal structural phase transitions with multiple phases with complex structures driven by charge density wave instabilities. I will also discuss how group theory, a powerful analytical tool, can be used in combination with DFT to map out the energy landscape and the phase diagram of these compounds. I will discuss how group theory can also help identify different “loop currents”, which are exotic phenomena proposed to exist in the Kagome metals, and hence resolve disagreements between different experimental observations. I will conclude by speculating about how loop currents also give rise to nonreciprocal optical phenomena which can be relevant for technological applications.

Bio. Turan Birol is an associate professor of chemical engineering and materials science at the University of Minnesota. He received his BS, MS, and PhD degrees from METU, Koc, and Cornell Universities respectively, and worked as a postdoctoral research associate at the Condensed Matter Theory group in Rutgers University before joining the University of Minnesota in 2016. Birol is currently a member of the University of Minnesota Materials Research Science and Engineering Center (MRSEC) and the  Center for Quantum Materials (CQM). His research interests lie on the intersection of condensed matter physics, structural chemistry, and materials science; where he uses first-principles computational tools to study and discover novel realizations of exotic phenomena in crystalline compounds, with a focus on transition metal oxides.