Strain-induced pseudo magnetic fields offer the possibility of realizing zero
magnetic field Quantum Hall effect in graphene, possibly up to room
temperature, representing a promising avenue for lossless charge transport
applications. Strain engineering on graphene has been achieved via random
nanobubbles or artificial nanostructures on the substrate, but the highly
localized and non-uniform pseudomagnetic fields can make spectroscopic probes
of electronic structure difficult. Heterostructure engineering offers an
alternative approach: By stacking graphene on top of another van der Waals
material with large lattice mismatch at a desired twist angle, it is possible
to generate large strain-induced pseudo magnetic fields uniformly over the
entire heterostructure. Here, we report using nano-angle resolved photoemission
spectroscopy (nano-ARPES) to probe the electronic bandstructure of a
graphene/black phosphorus heterostructure (G/BP). By directly measuring the
iso-energy contours of graphene and black phosphorus we determine a twist angle
of 20-degrees in our heterostructure. High-resolution nano-ARPES of the
graphene bands near the Fermi level reveals the emergence of flat bands located
within the Dirac cone. The spacing of the flat bands is consistent with Landau
level formation in graphene, and corresponds to a pseudo-field of 11.36 T. Our
work provides a new way to study quantum Hall phases induced by strain in 2D
materials and heterostructures