  Twisted bilayer graphene (tBLG) provides a fascinating platform for
engineering flat bands and inducing correlated phenomena. By designing the
stacking architecture of graphene layers, twisted multilayer graphene can
exhibit different symmetries with rich tunability. For example, in twisted
monolayer-bilayer graphene (tMBG) which breaks the C2z symmetry, transport
measurements reveal an asymmetric phase diagram under an out-of-plane electric
field, exhibiting correlated insulating state and ferromagnetic state
respectively when reversing the field direction. Revealing how the electronic
structure evolves with electric field is critical for providing a better
understanding of such asymmetric field-tunable properties. Here we report the
experimental observation of field-tunable dichotomic electronic structure of
tMBG by nanospot angle-resolved photoemission spectroscopy (NanoARPES) with
operando gating. Interestingly, selective enhancement of the relative spectral
weight contributions from monolayer and bilayer graphene is observed when
switching the polarity of the bias voltage. Combining experimental results with
theoretical calculations, the origin of such field-tunable electronic
structure, resembling either tBLG or twisted double-bilayer graphene (tDBG), is
attributed to the selectively enhanced contribution from different stacking
graphene layers with a strong electron-hole asymmetry. Our work provides
electronic structure insights for understanding the rich field-tunable physics
of tMBG.
