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

TL;DR

This study investigates twisted MoS2 bilayers near 0° using microscopy and spectroscopy, revealing large moiré potentials, lattice reconstruction effects, and intrinsic vertical polarization, advancing understanding of interfacial ferroelectricity.

Contribution

It provides the first detailed microscopic analysis of lattice reconstruction, moiré potential, and polarization effects in near-zero twist angle MoS2 bilayers.

Findings

Large moiré potential of 100-200 meV for angles <3°

Lattice reconstruction leads to large triangular domains with rhombohedral stacking

Bias-dependent asymmetry indicates intrinsic vertical polarization

Abstract

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{\deg} using Scanning Tunneling Microscopy/Spectroscopy. We investigate the twist angle-dependence of the moir\'e pattern which is dominated by lattice reconstruction for small angles (<2{\deg}) leading to large triangular domains with rhombohedral stacking. Local spectroscopy measurements reveal a large moir\'e-potential strength of 100-200 meV for angles <3{\deg}. 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.