Scanning tunneling microscopy of van Hove singularities in small angle twisted bilayer graphene*

Electronic properties of stacked van der Waals bilayers critically depend on the twist angle between the monolayers. A famous example of this effect is the observation of superconductivity and strongly correlated insulating phases in twisted bilayer graphene (TBG) where the two graphene monolayers are twisted by the so-called magic angle (~1.1°). This system supports electronic bands that are almost completely non-dispersive (flat), which gives rise to strong electronic correlation effects. We use scanning tunneling microscopy and spectroscopy to track the positions of van Hove singularities originating from the flat bands in gated TBG for the range of twist angles from 1° to 3°. We find that close to magic angle values the van Hove singularities are strongly modified when the flat bands cross the Fermi level.