Multipole mixing in spin polarization of Auger electrons following single-photon ionization of boronlike ions

Spin polarization of Auger electrons emitted in the nonradiative decay following 1s single-photon ionization of boronlike ions is studied using the density-matrix theory. Special attention is paid to the multipole mixing effect of the ionizing field on the spin polarization. It is found that the effect significantly weakens the spin polarization for heavy ions, which becomes more pronounced for heavier ions. Such a depolarization effect is analogous to but stronger than that observed in linear polarization of x-ray photons [Phys. Rev. Lett.105, 243002 (2010)10.1103/PhysRevLett.105.040403]. It provides evidence of depolarization in the spin polarization of Auger electrons. The obtained spin polarization and multipole mixing contribution are sufficiently large to be observed using a Mott polarimeter combined with an advanced light source, which could provide novel insights into electron-photon interaction in the presence of strong Coulomb fields. Beyond the fundamental significance, the finding holds potential applications in surface and material science due to the close connection between the spin polarization of Auger electrons and the magnetic properties of matter.