  We used density functional theory to investigate the lateral heteromonolayers
of WTe2 and MoTe2. We confirmed that topologically nontrivial and trivial
phases are energetically favored for the WTe2 and MoTe2 monolayers, taken out
of bulk Td-WTe2 and 2H-MoTe2, respectively. We considered heteromonolayers
consisting of these stable building blocks. In the Td-WTe2 and 2H-MoTe2
heteromonolayers with the interfaces oriented perpendicular to the dimer chains
of W atoms in Td-WTe2 (y direction), two pairs of helical (quantum spin Hall
[QSH]) states, one at each interface, connect the valence and conduction bands.
The strain induced by the large lattice mismatch of the two materials in the y
direction widens the band gap of the QSH insulator of the Td-WTe2 monolayer and
is essential for electronic applications. Furthermore, one-dimensional channels
embedded in the layer can help avoid chemical degradation from the edges and
facilitate the densification of conducting channels. For the heteromonolayer
with interfaces in the x direction, the difference in atomic structure between
the two interfaces due to low symmetry creates an energy difference between two
helical states and a potential gradient in the wide band gap 2H-MoTe2 region,
resulting in various interface localized bands.
