  A quantum spin hall insulator(QSHI) is manifested by its conducting edge
channels that originate from the nontrivial topology of the insulating bulk
states. Monolayer 1T'-WTe2 exhibits this quantized edge conductance in
transport measurements, but because of its semimetallic nature, the coherence
length is restricted to around 100 nm. To overcome this restriction, we propose
a strain engineering technique to tune the electronic structure, where either a
compressive strain along a axis or a tensile strain along b axis can drive
1T'-WTe2 into an full gap insulating phase. A combined study of molecular beam
epitaxy and in-situ scanning tunneling microscopy/spectroscopy then confirmed
such a phase transition. Meanwhile, the topological edge states were found to
be very robust in the presence of strain.
