Quantum spin Hall state in monolayer 1T’-TMDCs*

Quantum spin Hall (QSH) insulator, also known as 2D topological insulator (TI), hosts quantized helical edge state, which is a superior candidate to construct artificial 1D superconductor utilizing the superconductivity proximity effect. Among the rapidly developing 2D TI family, group VI transition metal dichalcogenides (TMDCs) in 1T’ structural phases are unique in their van der Waals layered structure, which can be easily integrated into vertical heterostructures. Bottom-up synthesis of monolayer 1T’-TMDCs (WTe₂, WSe₂ and MoTe₂) on graphitized SiC substrate were achieved using molecular beam epitaxy. Together with theoretical calculation and ARPES measurement, the characteristic signatures of QSH states such as band inversion and bulk gap opening have been confirmed in 1T’-WTe₂ and WSe₂ [1, 2]. Scanning tunneling spectroscopy (STS) measurements further provide evidence for the robust edge states reside in the bulk gap. It is also found that, although conduction and valence band degeneracy is lifted in 1T’-MoTe₂, the spin-orbital coupling is not strong enough to further separate them, leaving 1T’-MoTe₂ a semimetal [3].

[1] S. Tang et al., Nature Physics 13, 683 (2017).
[2] M. M. Ugeda et al., Nature Communications 9, 3401 (2018).
[3] S. Tang et al., APL Mater. 6, 026601 (2018).