Large-Scale Mapping of Moire Superlattices by Hyperspectral Raman Imaging

Moire superlattices can induce correlated-electronic phases in twisted van der Waals materials: strongly correlated quantum phenomena emerge, such as superconductivity and the Mott-insulating state. However, moire superlattices produced through artificial stacking can be quite inhomogeneous, which hampers the development of a clear correlation between the moire period and the emerging electrical and optical properties. Here, it is demonstrated in twisted-bilayer transition-metal dichalcogenides that low-frequency Raman scattering can be utilized not only to detect atomic reconstruction, but also to map out the inhomogeneity of the moire lattice over large areas. The method is established based on the finding that both the interlayer-breathing mode and moire phonons are highly susceptible to the moire period and provide characteristic fingerprints. Hyperspectral Raman imaging visualizes microscopic domains of a 5 degrees twisted-bilayer sample with an effective twist-angle resolution of about 0.1 degrees. This ambient methodology can be conveniently implemented to characterize and preselect high-quality areas of samples for subsequent device fabrication, and for transport and optical experiments.

Automated summary

Low-frequency Raman scattering can detect atomic reconstruction and map out the inhomogeneity of moire lattice in twisted-bilayer transition-metal dichalcogenides. This method provides a way to study the emerging electrical and optical properties in moire superlattices.