  The crystallographic stacking order in multilayer graphene plays an important
role in determining its electronic structure. In trilayer graphene,
rhombohedral stacking (ABC) is particularly intriguing, exhibiting a flat band
with an electric-field tunable band gap. Such electronic structure is distinct
from simple hexagonal stacking (AAA) or typical Bernal stacking (ABA), and is
promising for nanoscale electronics, optoelectronics applications. So far clean
experimental electronic spectra on the first two stackings are missing because
the samples are usually too small in size (um or nm scale) to be resolved by
conventional angle-resolved photoemission spectroscopy (ARPES). Here by using
ARPES with nanospot beam size (NanoARPES), we provide direct experimental
evidence for the coexistence of three different stackings of trilayer graphene
and reveal their distinctive electronic structures directly. By fitting the
experimental data, we provide important experimental band parameters for
describing the electronic structure of trilayer graphene with different
stackings.
