Moire Potential, Lattice Relaxation and Layer Polarization in Marginally Twisted MoS2 Bilayers

Artificially twisted heterostructures of semiconducting transition metal dichalcogenides (TMDs) offer unprecedented control over their electronic and optical properties via the spatial modulation of interlayer interactions and structural reconstruction. Here we study twisted MoS2 bilayers in a wide range of twist angles near 0° using Scanning Tunneling Microscopy/Spectroscopy. We investigate the twist angle-dependence of the moiré pattern which is dominated by lattice reconstruction for small angles (<2°) leading to large triangular domains with rhombohedral stacking. Local spectroscopy measurements reveal a large moiré-potential strength of 100-200 meV for angles <3°. In reconstructed regions we see a bias-dependent asymmetry between neighboring triangular domains which we relate to the vertical polarization which is intrinsic to rhombohedral stacked TMDs. This viewpoint is urther supported by spectroscopy maps and ambient Piezoresponse measurements. Our results provide a microscopic perspective on this new class of interfacial ferroelectrics and can offer clues for designing novel heterostructures which harness this effect.