The 380th forum: New routes to topological materials
Department of Physics, Tokyo Institute of Technology
Shuichi Murakami obtained his Ph. D.(1999) degree from the University of Tokyo. He moved to Tokyo Institute of Technology as an associate professor in 2007 and became a professor in the Department of Physics and in Materials Research Center for Element Strategy in 2012. He has been working on theories of spintronics and topological phenomena in condensed matter physics. He received various prizes, including Sir Martin Wood Prize in 2010, IBM Japan Science Prize in 2011, JSPS Prize in 2012, and APS Fellow in 2017.
Topological materials have been attracting much interest in condensed matter physics. It is now well established how to determine whether a given material is topological or not, and how to find a number of topological materials from materials databases. Meanwhile it is a different task to understand physical origins of their topological nature. In my presentation, we explain a series of our works to understand their origins from various theoretical viewpoints [1-8]. For example, we studied how the topological-nontopological phase transitions occur in inversion asymmetric spinful systems [2-4], and it always accompanies topological semimetal phases in between the two phases. One can use this theory for search of topological semimetals [3,4].
One can also have physical insight towards topological materials from the nature and structure of chemical bonding in crystals [5-8]. For example, we propose that electrides, in which electrons serve as anions, are good candidates for topological materials [5,6,8], because band inversions can easily occur in these materials. Indeed, one can find various topological materials, such as topological insulators [5,8], nodal-line semimetals [5,8], and higher-order topological insulators .
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 M. Hirayama, S. Matsuishi, H. Hosono, and S. Murakami, Phys. Rev. X 8, 031067 (2018).
 M. Hirayama, R. Takahashi, S. Matsuishi, H. Hosono, and S. Murakami, preprint (2019).
 M. Hirayama, R. Okugawa, T. Miyake, and S. Murakami, Nat. Commun. 8, 14022 (2017).
 Y. Aihara, M. Hirayama, S. Murakami, preprint (2019).
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