  Despite various novel broken symmetry states have been revealed in bilayer
graphene (BLG) experimentally, the atomic-scale spectroscopic investigation has
been greatly limited. Here, we study high-resolution spectroscopic
characteristics of high-quality BLG and observe rich broken-symmetry-induced
Landau level (LL) splittings, including valley, spin and orbit, by using
ultralow-temperature and high-magnetic-field scanning tunneling microscopy and
spectroscopy (STM and STS). Our experiment demonstrates that both the spin and
orbital splittings of the lowest n = (0,1) LL depend sensitively on its filling
and exhibit an obvious enhancement at partial-filling states. More
unexpectedly, the splitting of a fully-filled and valley-polarized LL is also
enhanced by partial filling of the LL with the opposite valley. These results
reveal significant many-body effects in this system. At half filling of the n =
(0,1) LL (filling factor v = 0), a single-particle intermediate v = 0 phase,
which is the transition state between canted antiferromagnetic and
layer-polarized states in the BLG, is measured and directly visualized at the
atomic scale. Our atomic-scale STS measurement gives direct evidence that this
intermediate v = 0 state is the predicted orbital-polarized phase.
