Parallel and antiparallel angular momentum transfer of circularly polarized light to photoelectrons and Auger electrons at the Ni L3 absorption threshold

Abstract

We report the investigation of the angular momentum transfer of light to photoelectrons and Auger electrons at the Ni ${L}_{3}$ absorption threshold. Upon core-level excitation by circularly polarized light, the angular momentum of light, or helicity, is transferred to the emitted photoelectron. The angular momentum of the emitted photoelectron (${m}_{\mathrm{f}}$) is the sum of the helicity ($\ensuremath{\sigma}$) and the orbital magnetic quantum number of the initial state (${m}_{\mathrm{i}}$). Here the quantization axis was defined as the direction along the incident light. This can be measured by the parallax shift of the forward focusing peak (FFP) direction in the photoelectron intensity angular distribution. At the absorption threshold, the excited core-level electron is promoted to a conduction-band state and the angular momentum of the light is partially transferred to Auger electrons. We measured photoelectron and Auger electron intensity angular distributions from the Ni(111) surface at the ${L}_{3}$ absorption threshold. We observed a significant angular circular dichroism of the $[101]$ FFP for the ${L}_{3}{M}_{4,5}{M}_{4,5}$ Auger electrons. Furthermore, we discovered non-negligible reversal angular circular dichroism contrasts for the triplet components in the case of the ${L}_{3}{M}_{2,3}{M}_{4,5}$ Auger electrons, suggesting that the angular momentum of light was transferred to the emitted electron in the antiparallel way.