  Moire superlattices formed in van der Waals heterostructures due to twisting,
lattice mismatch and strain present an opportunity for creating novel
metamaterials with unique properties not present in the individual layers
themselves. Ferroelectricity for example, arises due to broken inversion
symmetry in twisted and strained bilayers of 2D semiconductors with stacking
domains of alternating out-of-plane polarization. However, understanding the
individual contributions of twist and strain to the formation of topological
polar nanostructures remains to be established and has proven to be
experimentally challenging. Inversion symmetry breaking has been predicted to
give rise to an in-plane component of polarization along the domain walls,
leading to the formation of a network of topologically non-trivial merons
(half-skyrmions) that are Bloch-type for twisted and Neel-type for strained
systems. Here we utilise angle-resolved, high-resolution vector piezoresponse
force microscopy (PFM) to spatially resolve polarization components and
topological polar nanostructures in marginally twisted bilayer WSe2, and
provide experimental proof for the existence of topologically non-trivial
meron/antimeron structures. We observe both Bloch-type and Neel-type merons,
allowing us to differentiate between moire superlattices formed due to twist or
heterogeneous strain. This first demonstration of non-trivial real-space
topology in a twisted van der Waals heterostructure opens pathways for
exploring the connection between twist and topology in engineered nano-devices.
