Visualization of the flat electronic band in twisted bilayer graphene near the magic angle twist

TL;DR

This paper reports the direct visualization of the flat moire miniband in twisted bilayer graphene near the magic angle using nanoARPES, confirming the presence of flat dispersion crucial for correlated electronic phases.

Contribution

The study provides the first direct momentum-space observation of the flat miniband in tBLG near the magic angle using nanoARPES at room temperature.

Findings

Confirmed the existence of a flat moire band near charge neutrality.

Used nanoARPES to measure local electronic structure.

Demonstrated flat band presence at room temperature.

Abstract

Bilayer graphene was theorized to host a moire miniband with flat dispersion if the layers are stacked at specific twist angles known as the magic angles. Recently, such twisted bilayer graphene (tBLG) with the first magic angle twist was reported to exhibit correlated insulating state and superconductivity, where the presence of the flat miniband in the system is thought to be essential for the emergence of these ordered phases in the transport measurements. Tunneling spectroscopy and electronic compressibility measurements in tBLG have revealed a van Hove singularity that is consistent with the presence of the flat miniband. However, a direct observation of the flat dispersion in the momentum-space of such moire miniband in tBLG is still elusive. Here, we report the visualization of the flat moire miniband by using angle-resolved photoemission spectroscopy with nanoscale resolution (nanoARPES). The high spatial resolution in nanoARPES enabled the measurement of the local electronic structure of the tBLG. We clearly demonstrate the existence of the flat moire band near the charge neutrality for tBLG close to the magic angle at room temperature.