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

Abstract

Monolayer (ML) 1T′-MoTe 2 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′-MoTe 2 via interfacing a 3D topological insulator Bi 2 Te 3 , facilitating the realization of pure 1T′ phase and even the band gap opening. It is further verified that the epi-grown ML 1T′-MoTe 2 on Bi 2 Te 3 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′-MoTe 2 . The results also reveal the nontrivial band topology in ML 1T′-MoTe 2 is preserved in 1T′-MoTe 2 /Bi 2 Te 3 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.

A comprehensive review on Bi2Te3‐based thin films: Thermoelectrics and beyond

“…[ 177 ] Our group has recently proposed a plausible road for the opening of the band gap in a monolayer of 1Tʹ‐MoTe 2 through the formation of a 1Tʹ‐MoTe 2 /Bi 2 Te 3 vdW‐type heterostructure and by utilizing the SOC proximity effect. [ 174 ] Our theoretical studies have revealed that strong interlayer interactions and the prominent charge transfer at the interface are the origins of the SOC proximity effect and the enhanced intrinsic SOC in such a heterostructure. The enhanced intrinsic SOC is the prerequisite for the band gap opening, and the calculated band gap for a monolayer of 1Tʹ‐MoTe 2 is ∼40 meV.…”

“…Reproduced from Ref. [174] Copyright 2021, John Wiley and Sons. (C) STM surface morphology and STS superconducting energy gap in Bi 2 Se 3 films grown on superconducting NbSe 2 substrates.…”

“…However, these theoretical calculations were not exactly verified by experiments because the ARPES spectra became very blurred upon dosing Cs on the surface of graphene. The other example shows the tendency of a band gap opening in a monolayer of 1Tʹ‐MoTe 2 grown on the Bi 2 Te 3 buffer layer, [ 174 ] as illustrated in Figure 9B. The monolayer 1Tʹ‐MoTe 2 is predicted to be a promising QSH phase, however, the pristine monolayer 1Tʹ‐MoTe 2 is a semimetal with the negative band gap.…”

Rational Manipulation of Epitaxial Strains Enabled Valence Band Convergence and High Thermoelectric Performances in Mg3Sb2 Films

“…Moreover, compared to the Δ CF , the Δ SOC varies slightly near the characteristic zone, indicating the lattice strain plays a minor role in modulating Δ SOC . Since the SOC could be tuned by doping or forming hetero‐structure, [ 56–58 ] one would expect to realize a triple‐degenerated VBM (i.e., VB1, VB2, and VB3 coinciding in energy) in Mg 3 Sb 2 through combined efforts of strain engineering and compositional adjustment.…”

“…Mater. 2023, 33, 2300154 could be tuned by doping or forming hetero-structure, [56][57][58] one would expect to realize a triple-degenerated VBM (i.e., VB1, VB2, and VB3 coinciding in energy) in Mg 3 Sb 2 through combined efforts of strain engineering and compositional adjustment.…”