  Layer stacking and crystal lattice symmetry play important roles in the band
structure and the Landau levels of multilayer graphene. ABA-stacked trilayer
graphene possesses mirror-symmetry-protected monolayer-like and bilayer-like
band structures. Broken mirror symmetry by a perpendicular electric field
therefore induces hybridization between these bands and various quantum Hall
phases emerge. We experimentally explore the evolution of Landau levels in
ABA-stacked trilayer graphene under electric field. We observe a variety of
valley and orbital dependent Landau level evolutions. These evolutions are
qualitatively well explained by considering the hybridization between multiple
Landau levels possessing close Landau level indices and the hybridization
between every third Landau level orbitals due to the trigonal warping effect.
These observations are consistent with numerical calculations. The combination
of experimental and numerical analysis thus reveals the entire picture of
Landau level evolutions decomposed into the monolayer- and bilayer-like band
contributions in ABA-stacked trilayer graphene.
