posted on 2022-12-28, 17:39authored byNikhil Tilak, Guohong Li, Takashi Taniguchi, Kenji Watanabe, Eva Y. Andrei
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 that is intrinsic to rhombohedral stacked
TMDs. This viewpoint is further supported by spectroscopy maps and
ambient piezoresponse measurements. Our results provide a microscopic
perspective of this new class of interfacial ferroelectrics and can
offer clues for designing novel heterostructures that harness this
effect.