Physics Colloquium: Topological Surface States in Dirac Semimetal α-Sn (Prof. Mingzhong Wu, Colorado State University)
Abstract: Topological Dirac semimetals represent a relatively newly-discovered topological quantum phase. In comparison with other topological Dirac semimetals, a-Sn is much more attractive because (1) it is a single-element material and is therefore relatively easy to grow, and (2) it can transform to other topological phases, such as a topological insulator or a Weyl semimetal, under certain strain or field conditions. This talk will report on recent experimental work on topological surface states in Dirac semimetal a-Sn thin films. The talk will consist of three parts. Part I will focus on magnetoresistance in a-Sn thin films that scales linearly with both magnetic and electric fields.1 Such bilinear magneto-electric resistance results from the spin-momentum locking of the topological surface states in a-Sn films. Part II will be on large damping enhancement in a ferromagnetic thin film due to topological surface states in an adjacent a-Sn thin film.2 It will be shown that an a-Sn film separated from a NiFe film by a Ag spacer can cause an extra damping in NiFe that is three times bigger than the intrinsic damping. Part III will report on current-induced magnetization switching in an a-Sn/Ag/CoFeB trilayer.3 Thanks to the surface states in a-Sn, the magnetization in CoFeB can be switched by a charge current at room temperature, without an external magnetic field. The data show that the switching is driven by topological surface states in a-Sn, rather than spin-orbit coupling in the bulk of a-Sn or current-produced heating. Taken together, these results suggest that, like topological insulators, the topological Dirac semimetal a-Sn may have promising applications in spintronics.
- “Large magneto-electric resistance in the topological Dirac semimetal a-Sn,” Yuejie Zhang, Vijaysankar Kalappattil, Chuanpu Liu, Steven S.-L. Zhang, Jinjun Ding, Uppalaiah Erugu, Jifa Tian, Jinke Tang, and Mingzhong Wu, submitted (2021).
- “Large damping enhancement in Dirac-semimetal – ferromagnetic-metal layered structures caused by topological surface states,” Jinjun Ding, Chuanpu Liu, Yuejie Zhang, Vijaysankar Kalappattil, Rui Yu, Uppalaiah Erugu, Jinke Tang, Haifeng Ding, Hua Chen, and Mingzhong Wu, Advanced Functional Materials 2021, 2008411 (2021).
- “Switching of a magnet by spin-orbit torque from a topological Dirac semimetal,” Jinjun Ding, Chuanpu Liu, Vijaysankar Kalappattil, Yuejie Zhang, Oleksandr Mosendz, Uppalaiah Erugu, Rui Yu, Jifa Tian, August DeMann, Stuart B. Field, Xiaofei Yang, Haifeng Ding, Jinke Tang, Bruce Terris, Albert Fert, Hua Chen, and Mingzhong Wu, Advanced Materials 2021, 2005909 (2021).
Biography: Mingzhong Wu received his Ph.D. in Solid State Electronics from Huazhong University of Science and Technology in China in 1999, joined the Colorado State University (CSU) faculty in 2007, and is currently the Professor of Physics and the Director of CSU’s “Program of Research and Scholarly Excellence” Designated Center for Advanced Magnetics. His current research areas include topological quantum materials, spintronics, magnetization dynamics, and nonlinear spin waves. He has authored over 160 technical papers and 4 book chapters; he has also co-edited a book on magnetic insulators. He served as an Editor for “IEEE Magnetics Letters” (2012- 2016), and is currently an Editor for “Physics Letters A” and “Journal of Alloys and Compounds.” He was the Education Committee Chair (2012-2015) and Finance Chair (2015-2018) of the IEEE Magnetics Society and is currently the Chair of the Technical Committee of the Society. He was named Professor Laureate by the College of Natural Sciences at CSU for 2019-2021. He was elected IEEE Fellow in 2021.