Strong Correlations in Magic Angle Twisted Bilayer Graphene Investigated by Scanning Tunneling Microscopy

Recent results on twisted bilayer graphene near the “magic” angle of 1.1 degrees reveal gate-tunable superconducting and correlated insulating states generally attributed to the flat band emerging from the moire superlattice and hybridization between the two layers. To date, the investigation of these states has been limited to bulk probes, inherently hindered by overall sample disorder and inhomogeneity. Using gated scanning tunneling microscopy and spectroscopy (STS), we directly locally investigate twisted bilayer graphene around the magic angle. Many theories have been proposed as to the precise band structure which causes the insulating and superconducting states to emerge, but the question remains for instance as to the size of the gap at charge neutrality and at half filling of the moire superlattices. We show the real experimental L-DOS probed by STS at and near the magic angle with gate tunable doping. Our results show the size of the gap at charge neutrality as well as the half filling state which enables a better understanding of the correlation effects leading to the insulating and superconducting states. Additionally, we study the effects of the local inhomogeneity which likely leads to the variable results observed in transport.