  Here we report the evolution of bulk band structure and surface states in
rare earth mono-bismuthides with partially filled f shell. Utilizing
synchrotron-based photoemission spectroscopy, we determined the
three-dimensional bulk band structure and identified the bulk band inversions
near the X points, which, according to the topological theory, could give rise
to nontrivial band topology with odd number of gapless topological surface
states. Near the surface Gamma bar point, no clear evidence for predicted
gapless topological surface state is observed due to its strong hybridization
with the bulk bands. Near the M bar point, the two surface states, due to
projections from two inequivalent bulk band inversions, interact and give rise
to two peculiar sets of gapped surface states. The bulk band inversions and
corresponding surface states can be tuned substantially by varying rare earth
elements, in good agreement with density-functional theory calculations
assuming local f electrons. Our study therefore establishes rare earth
mono-bismuthides as an interesting class of materials possessing tunable
electronic properties and magnetism, providing a promising platform to search
for novel properties in potentially correlated topological materials.
