Spectroscopic visualization of flat bands in magic-angle twisted monolayer-bilayer graphene: localization-delocalization coexisting electronic states

TL;DR

This study uses scanning tunneling microscopy to directly visualize and compare flat electronic bands in twisted monolayer-bilayer graphene and twisted bilayer graphene, revealing layer-resolved localization-delocalization coexistence.

Contribution

It provides the first direct visualization and comparison of flat bands in tMBG and tBG, demonstrating their layer-specific electronic states and validating theoretical predictions.

Findings

Confirmed existence of flat bands in tMBG via density of states peak

Flat-band bandwidth in tMBG is slightly narrower than in tBG

Discovered layer-resolved localization-delocalization coexistence in tMBG

Abstract

Recent transport studies have demonstrated the great potential of twisted monolayer-bilayer graphene (tMBG) as a new platform to host moir\'e flat bands with a higher tunability than twisted bilayer graphene (tBG). However, a direct visualization of the flat bands in tMBG and its comparison with the ones in tBG remain unexplored. Here, via fabricating on a single sample with exactly the same twist angle of ~1.13{\deg}, we present a direct comparative study between tMBG and tBG using scanning tunneling microscopy/spectroscopy. We observe a sharp density of states peak near the Fermi energy in tunneling spectroscopy, confirming unambiguously the existence of flat electronic bands in tMBG. The bandwidth of this flat-band peak is found to be slightly narrower than that of the tBG, validating previous theoretical predictions. Remarkably, by measuring spatially resolved spectroscopy, combined with continuum model calculation, we show that the flat-band states in tMBG exhibit a unique layer-resolved localization-delocalization coexisting feature, which offers an unprecedented possibility to utilize their cooperation on exploring novel correlation phenomena. Our work provides important microscopic insight of flat-band states for better understanding the emergent physics in graphene moir\'e systems.