  Van der Waals (vdW) heterostructures formed by 2D atomic crystals provide a
powerful approach towards designer condensed matter systems. Incommensurate
heterobilayers with small twisting and/or lattice mismatch lead to the
interesting concept of Moir\'e superlattice, where the atomic registry is
locally indistinguishable from commensurate bilayers but has local-to-local
variation over long range. Here we show that such Moir\'e superlattice can lead
to periodic modulation of local topological order in vdW heterobilayers formed
by two massive Dirac materials. By tuning the vdW heterojunction from normal to
the inverted type-II regime via an interlayer bias, the commensurate
heterobilayer can become a topological insulator (TI), depending on the
interlayer hybridization controlled by the atomic registry between the vdW
layers. This results in mosaic pattern of TI regions and normal insulator (NI)
regions in Moir\'e superlattices, where topologically protected helical modes
exist at the TI/NI phase boundaries. By using symmetry based k.p and
tight-binding models, we predict that this topological phenomenon can be
present in inverted transition metal dichalcogenides heterobilayers. Our work
points to a new means of realizing programmable and electrically switchable
topological superstructures from 2D arrays of TI nano-dots to 1D arrays of TI
nano-stripes.
