Spatially Dependent Electronic Structures and Excitons in a Marginally Twisted Moire Superlattice of Spiral WS2

Twisted two-dimensional transition metal dichalcogenide (TMD) moire superlattices provide an additional degree of freedom to engineer electronic and optical properties. Nevertheless, controllable synthesis of marginally twisted homo TMD moire superlattices is still a challenge. Here, physical vapor deposition grown spiral WS 2 nanosheets are demonstrated to be a marginally twisted moire superlattice using scanning tunneling microscopy and spectroscopy. Periodic moire superlattices are found on the third layer (3L) and 4L of the spiral WS2 nanosheet owing to the marginally twisted alignment between two neighboring layers, resulting in a highly localized flat band near the valence band maximum. Their bandgap depends on atomic stacking configurations, which gives a good interpretation for split moire excitons using photoluminescence at 77 K. This work can benefit the development of twisted homo TMD moire superlattices and could promote the profound research of twisted TMDs in the prospective field, such as strongly correlated physics and twistronics.

Automated summary

This research demonstrates that spiral WS2 nanosheets are marginally twisted moire superlattices using scanning tunneling microscopy and spectroscopy. The periodic moire superlattices are found on the third and fourth layers, resulting in a localized flat band near the valence band maximum. The bandgap depends on atomic stacking configurations, providing a good explanation for split moire excitons observed through photoluminescence.