Tendency of Gap Opening in Semimetal 1T′-MoTe₂ with Proximity to a 3D Topological Insulator

Monolayer (ML) 1T′-MoTe₂ has attracted intensive interest as a fascinating quantum spin Hall (QSH) insulator. However, there are two critical aspects impeding its exploration and potential applications of QSH effects. One is its semimetallic feature with a negative band gap, leading to nontrivial edge channels annihilated by the bulk states. The other is its fabrication always accompanied by a mixed phase of 1T′ and 2H. Based on first-principles calculations, it is shown that the large work-function difference results in strong interlayer interactions and proximity effects in ML 1T′-MoTe₂ via interfacing a 3D topological insulator Bi₂Te₃, facilitating the realization of pure 1T′ phase and even the band gap opening. It is further verified that the epi-grown ML 1T′-MoTe₂ on Bi₂Te₃ is nearly in single phase. Furthermore, the measurements of angle resolved photoemission spectroscopy and scanning tunneling spectroscopy confirm the obvious separated-tendency of conduction and valence bands as well as the strong metallic edge states in ML 1T′-MoTe₂. The results also reveal the nontrivial band topology in ML 1T′-MoTe₂ is preserved in 1T′-MoTe₂/Bi₂Te₃ heterostructure. This work offers a promising candidate to realize QSH effects and provides guidance for controlling the nontrivial band gap opening by proximity effects in van der Waals engineering.