Abstract
Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe2 single layer with the 1T′ structure that does not exist in the bulk form of WSe2. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observe a gap of 129 meV in the 1T′ layer and an in-gap edge state located near the layer boundary. The system′s 2D TI characters are confirmed by first-principles calculations. The observed gap diminishes with doping by Rb adsorption, ultimately leading to an insulator–semimetal transition. The discovery of this large-gap 2D TI with a tunable band gap opens up opportunities for developing advanced nanoscale systems and quantum devices.
Highlights
Two-dimensional (2D) topological insulators (TIs) are promising platforms for lowdissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult
The edge states are spin polarized by spin–orbit coupling in a chiral configuration relative to the momentum and the edge normal; they are protected by timereversal symmetry and robust against weak disorder
We show that single layers of WSe2 can be prepared instead in the 1T′ phase, which is topological with a gap of 129 meV based on angle-resolved photoemission spectroscopy (ARPES) experiments and 116 meV based on G0W0 calculations
Summary
Two-dimensional (2D) topological insulators (TIs) are promising platforms for lowdissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. We show that single layers of WSe2 can be prepared instead in the 1T′ phase, which is topological with a gap of 129 meV based on angle-resolved photoemission spectroscopy (ARPES) experiments and 116 meV based on G0W0 calculations. This gap is more than twice as large as that reported for 1T′ WTe217 and, it can be tuned with surface doping to undergo an insulator–semimetal transition. Single-layer 1T′ WSe2 is an excellent candidate for developing spintronics based on the QSH effect
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