Coexistence of biholes and electron-bihole complexes in the photoemission final state in cuprous halides

Abstract

It has been found that the valence-band satellite and the Cu $M_2$,3${\mathrm{M}}_4$,5${\mathrm{M}}_4$,5 super-Coster-Kronig lines appear simultaneously in the photoelectron spectra of cuprous halides observed by excitations above the threshold of the 3p electron of copper. This is ascribed to the coexistence of biholes and electron-bihole complexes (‘‘trions’’) in the final state of photoemission. The satellite exists even far below the Cu 3p threshold and is strongly enhanced resonantly above the threshold, but the main band is enhanced quite weakly. The Cu $M_2$,3${\mathrm{M}}_4$,5${\mathrm{M}}_4$,5 super-Coster-Kronig lines occur always on the high-binding-energy side of the satellite. They appear at excitation energies a few electron volts higher than those at which the satellite starts to be enhanced. In the vicinity of their onset these super-Coster-Kronig lines do not have a constant kinetic energy but a constant binding energy, in accordance with a recently reported theory. The super-Coster-Kronig lines are also enhanced near the thresholds but their excitation profiles are not similar to the partial photoelectric yield spectrum, suggesting a kind of resonance process. All of these aspects of the emergence of the satellite and the super-Coster-Kronig lines are consistent with the ‘‘trion’’ model of the satellite, viz., two bound holes (i.e., a bihole) with a trapped electron. Related effective Coulomb energies and relaxation energies are estimated along with those of the Br $M_4$,5${\mathrm{N}}_2$,3${\mathrm{N}}_2$,3 and I $N_4$,5${\mathrm{O}}_2$,3${\mathrm{O}}_2$,3 Auger lines.