Quantum spin Hall state in monolayer 1T’ TMDcs

QSH state or 2D topological state is a topologically nontrivial quantum state that features quantized Hall conductance in the absence of a magnetic field. We successfully synthesized stable 2D van der Waals materials that host quantum spin Hall insulators, monolayer 1T’-TMDcs, using molecular-beam- epitaxy (MBE). Together with the theoretical calculation, subsequent in situ ARPES measurements reveals the characteristic signatures of a QSH state in the electronic structure, i.e., a band inversion and a band gap opening in monolayer 1T’-WTe 2 . Another essential evidence of QSH phase came from a STM measurements, which observed confined edge states. Similar cases are also achieved in 1T’-WSe 2 with subtle differences in the details of electronic structure and larger nontrivial bulk gap. We have also found that 1T’-MoTe 2 is a semimetal with a significant overlap between inverted valence and conduction bands rather than a QSH insulator.