Transition metal compounds with partially filled d-orbitals may have unique physical properties due to the large spin-orbit coupling (SOC) and correlation effect. In this talk, Dr. Sheng will show negative SOC topological insulator (TI), Weyl/Dirac semimetal and hourglass Dirac nodal chain materials. It is found that Cu2S with antifluorite structure is a topological insulator with negative SOC . Cu2Se and CuAgSe are topological semimetals with positive SOC similar to HgTe. By applying uniaxial strain, CuAgSe becomes an idea Weyl semimetal with four pairs of Weyl nodes. Contrasting spin helicities and hybrid surface states were discovered in these materials. For wurtzite structure materials, TlN is a TI with negative SOC , while CaAgBi is Dirac semimetal with positive SOC. Moreover, he found hybrid Dirac-type dispersions in CaAgBi with positive SOC, including essential and accidental, type-I and type-II Dirac fermions . For magnetic materials, he will report a two-dimensional intrinsic quantum anomalous Hall insulator in a monolayer 5d transition metal trichloride OsCl3, and a Weyl-loop half-metal Li3(FeO3)2. Finally, he will report a new topological phase Hourglass Dirac Nodal Chain Metal and its materials realization in ReO2, where both nonsymmorphic symmetry and large SOC in d-orbitals play important roles to form such nodal chain phase .
Dr. Sheng Xianlei is an assistant professor in School of Physics of Beihang University in China, and a visiting scholar in RLQM of SUTD. He received his B.S. degree from Xidian University in 2006. From 2006 to 2011, he was studying in the University of Chinese Academy of Sciences, and obtained his Ph.D. in condensed matter physics. Then, he worked as a postdoctoral researcher and visiting scholar in several institutions including California State University Northridge, Institute of Physics Chinese Academy of Sciences, and University of Delaware. In 2015, he joined Beihang University as a Lecturer and now as an Assistant Professor. He conducted research at RLQM of SUTD from Oct. 2016 to Sep. 2017, and from Oct. 2018 to now. Recently, his research focuses on topological materials study from first-principles calculation. He has co-authored more than 30 papers.