Imaging Electronic Correlations in Twisted Bilayer Graphene near the Magic Angle

TL;DR

This study uses scanning tunneling microscopy to explore how electronic correlations and flat band deformations in twisted bilayer graphene near the magic angle lead to correlated insulating states and nematic ordering, revealing the importance of interactions.

Contribution

It provides the first detailed local probe of correlation effects and flat band deformation in twisted bilayer graphene near the magic angle, highlighting new correlated regimes.

Findings

Observation of flat band deformation near Fermi level.

Detection of correlated insulating gaps at half filling.

Identification of a new correlated regime with enhanced flat band splitting.

Abstract

Twisted bilayer graphene with a twist angle of around 1.1{\deg} features a pair of isolated flat electronic bands and forms a strongly correlated electronic platform. Here, we use scanning tunneling microscopy to probe local properties of highly tunable twisted bilayer graphene devices and show that the flat bands strongly deform when aligned with the Fermi level. At half filling of the bands, we observe the development of gaps originating from correlated insulating states. Near charge neutrality, we find a previously unidentified correlated regime featuring a substantially enhanced flat band splitting that we describe within a microscopic model predicting a strong tendency towards nematic ordering. Our results provide insights into symmetry breaking correlation effects and highlight the importance of electronic interactions for all filling factors in twisted bilayer graphene.