  Graphene/h-BN has emerged as a model van der Waals heterostructure, and the
band structure engineering by the superlattice potential has led to various
novel quantum phenomena including the self-similar Hofstadter butterfly states.
Although newly generated second generation Dirac cones (SDCs) are believed to
be crucial for understanding such intriguing phenomena, so far fundamental
knowledge of SDCs in such heterostructure, e.g. locations and dispersion of
SDCs, the effect of inversion symmetry breaking on the gap opening, still
remains highly debated due to the lack of direct experimental results. Here we
report first direct experimental results on the dispersion of SDCs in 0$^\circ$
aligned graphene/h-BN heterostructure using angle-resolved photoemission
spectroscopy. Our data reveal unambiguously SDCs at the corners of the
superlattice Brillouin zone, and at only one of the two superlattice valleys.
Moreover, gaps of $\approx$ 100 meV and $\approx$ 160 meV are observed at the
SDCs and the original graphene Dirac cone respectively. Our work highlights the
important role of a strong inversion symmetry breaking perturbation potential
in the physics of graphene/h-BN, and fills critical knowledge gaps in the band
structure engineering of Dirac fermions by a superlattice potential.
