The discovery of quantum spin Hall e ect engendered a new chapter of topological materials research in condensed matter physics and materials science. In this talk, I will introduce some of our recent theoretical works about the topological phases in 2D and 3D transition metal chalcogenides. We predict monolayer MX2 (M=Mo, W; X=S, Se, Te) of 1T’ structure could realize quantum spin Hall insulator. Moreover, their topology can be easily tuned by external electric field, which motivated us to propose a new type of transistor, called topological eld transistor. More recently, we found another new class of transition metal chalcogenides MM’Te4 (M=Nb, Ta; M’=Ir, Rh) could be quantum spin Hall insulators in 2D and Weyl semimetals in 3D. I will also discuss some recent transport, ARPES and STM experiments on monolayer WTe2, where many of the observations are consistent with monolayer WTe2 being a 2D TI.
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