Observation of flat $\Gamma$ moir\'e bands in twisted bilayer WSe$_2$

TL;DR

This study reveals flat moiré bands originating from the monolayer Γ states in twisted bilayer WSe₂, providing insights into the electronic structure relevant for correlated phases in transition metal dichalcogenides.

Contribution

It provides direct experimental evidence of Γ-derived flat bands in twisted WSe₂ and quantifies the moiré potential, advancing understanding of moiré physics in TMDs.

Findings

Identification of a split-off flat band from Γ states

Quantification of the moiré potential from experimental data

Proximity of valence band maximum to the flat band from K-states

Abstract

The recent observation of correlated phases in transition metal dichalcogenide moir\'e 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 moir\'e superlattice effects in 57.4$^{\circ}$ twisted WSe$_2$ (tWSe$_2$). Our data reveal a split-off flat band that derives from the monolayer $\Gamma$ states. Using advanced data analysis, we directly quantify the moir\'e potential from our data. We further demonstrate that the global valence band maximum in tWSe$_2$ 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 $\Gamma$-valley flat bands might be involved in the correlated physics of twisted WSe$_2$.