  Electronic structures of single crystalline black phosphorus were studied by
state-of-art angleresolved photoemission spectroscopy. Through high resolution
photon energy dependence measurements, the band dispersions along out-of-plane
and in-plane directions are experimentally determined. The electrons were found
to be more localized in the ab-plane than that is predicted in calculations.
Beside the kz-dispersive bulk bands, resonant surface state is also observed in
the momentum space. Our finds strongly suggest that more details need to be
considered to fully understand the electronic properties of black phosphorus
theoretically.
