  In twisted h-BN/graphene heterostructures, the complex electronic properties
of the fast-traveling electron gas in graphene are usually considered to be
fully revealed. However, the randomly twisted heterostructures may also have
unexpected transition behaviors, which may influence the device performance.
Here, we study the twist angle-dependent coupling effects of h-BN/graphene
heterostructures using monochromatic electron energy loss spectroscopy. We find
that the moir\'e potentials alter the band structure of graphene, resulting in
a redshift of the intralayer transition at the M-point, which becomes more
pronounced up to 0.25 eV with increasing twist angle. Furthermore, the twisting
of the Brillouin zone of h-BN relative to the graphene M-point leads to tunable
vertical transition energies in the range of 5.1-5.6 eV. Our findings indicate
that twist-coupling effects of van der Waals heterostructures should be
carefully considered in device fabrications, and the continuously tunable
interband transitions through the twist angle can serve as a new degree of
freedom to design optoelectrical devices.
