Tunable Electronic Structure and Surface States in Rare Earth Mono-Bismuthides with Partially Filled f Shell

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.