Resonant photoemission in single-crystal black phosphorus

Resonant photoemission in single-crystal black phosphorus has been reinvestigated in detail by high-resolution spectroscopy. Partial-yield, valence-band, and constant-initial-state spectra were measured in the 2p core-exciton excitation region. We have confirmed two types of resonances at the 2p core threshold: one is a strong core-exciton-induced resonance with two final valence holes and the other is a weak Fano-type resonance. The Fano-type resonance is preferentially associated with the lower-energy spin-orbit doublet (A-A’) of the core excitons (A-A’ and B-B’ being separated by 0.2 eV). This result elucidates the difference of the degree of localization of the core excitons, A-A’ and B-B’, and rules out the possibility that the L2,3VV Auger tail is solely responsible for the resonance profile.