Direct STM Measurements of R- and H-type Twisted MoSe2/WSe2 Heterostructures

TL;DR

This study uses STM to measure electronic band modulations in twisted MoSe2/WSe2 heterostructures at near 0 and 60 degrees, revealing twist-dependent band gap variations and electron localization.

Contribution

It provides the first direct STM measurements of band gap modulations in R- and H-type twisted MoSe2/WSe2 heterostructures, confirming theoretical predictions.

Findings

Band gap modulation observed in both stacking types

Larger modulation in R-type than H-type structures

Electrons show different localization at valence and conduction bands

Abstract

When semiconducting transition metal dichalcogenides heterostructures are stacked the twist angle and lattice mismatch leads to a periodic moir\'e potential. As the angle between the layers changes, so do the electronic properties. As the angle approaches 0- or 60-degrees interesting characteristics and properties such as modulations in the band edges, flat bands, and confinement are predicted to occur. Here we report scanning tunneling microscopy and spectroscopy measurements on the band gaps and band modulations in MoSe2/WSe2 heterostructures with near 0 degree rotation (R-type) and near 60 degree rotation (H-type). We find a modulation of the band gap for both stacking configurations with a larger modulation for R-type than for H-type as predicted by theory. Furthermore, local density of states images show that electrons are localized differently at the valence band and conduction band edges.