Flat Γ Moiré Bands in Twisted Bilayer WSe2

Combined real- and momentum-space mapping of moiré superlattices reveals intriguing flat-band physics of certain van der Waals materials.

The recent observation of correlated phases in transition metal dichalcogenide moiré systems at integer and fractional filling promises new insight into metal-insulator transitions and the unusual states of matter that can emerge near such transitions. Here, we combine real- and momentum-space mapping techniques to study moiré superlattice effects in 57.4° twisted WSe2 (tWSe2). Our data reveal a split-off flat band that derives from the monolayer Γ states. Using advanced data analysis, we directly quantify the moiré potential from our data. We further demonstrate that the global valence band maximum in tWSe2 is close in energy to this flat band but derives from the monolayer K states which show weaker superlattice effects. These results constrain theoretical models and open the perspective that Γ-valley flat bands might be involved in the correlated physics of twisted WSe2.

G. Gatti, J. Issing et al., Phys. Rev. Lett. 131, 046401 (2023)