Investigation of moiré inhomogeneity in twisted transition metal dichalcogenide bilayers

Twist angle is an important design parameter in two-dimensional (2D) moiré materials. Much of the novel physical phenomena found in twisted homobilayers of 2D atomic crystals are highly sensitive to the twist angle, or equivalently, the moiré superlattice periodicity. It has been suggested that local variations of twist angle may be introduced in moiré materials due to factors including anisotropy inherent in the fabrication process and structural distortion due to the interaction between constituent monolayers. As a result, moiré inhomogeneity is introduced in moiré crystals, in analogy to atomic inhomogeneity in regular crystals. In this talk, we will report our investigation of moiré inhomogeneity at mesoscopic scales in twisted transition metal dichalcogenide (TMD) homobilayers probed by scanning rotational anisotropy second harmonic generation (RA-SHG) microscopy. We will leverage the high angular resolution and the intensity sensitivity of our RA-SHG microscopy to map out the twist angle variations and interlayer coupling of the twisted TMD bilayers. Furthermore, we will compare this moiré inhomogeneity mapping with the spatially dependent exciton landscape. Finally, we will comment on frequency-resolved SHG in conjunction with moiré electronic band structures.