The magnetic exciton revealed in EuS by resonant inelastic x-ray scattering


We report the valence-to-core resonant inelastic x-ray scattering
(RIXS) of EuS measured at the L3 edge of europium. The obtained data
reveal two sets of excitations: one set is composed of a hole in the
S 3p bands and an electron excited to extended Eu 5d band states, the
other is made up from a hole in the Eu 4f states and an electron in
localized Eu 5d states bound to the 4f hole by its Coulomb
potential. The delocalized excitations arise from the dipole-allowed
5d → 2p emissions, whereas the localized excitations result from the
dipole-forbidden (quadrupole-allowed) 4f → 2p emissions. Both these
emission channels have a comparable intensity thanks to a small number
of occupied 5d states (approximately 0.6) combined with a large number
of occupied 4f states (seven). We identify the localized electron-hole
pairs with the “magnetic excitons” suggested in the past as an
interpretation of the sharp features seen in the optical absorption
spectra of europium chalcogenides. Our observations provide a direct
experimental evidence of these excitons which has been missing up to
now. The talk will focus on the theoretical interpretation of the
spectra using a combination of the LDA+DMFT method, LDA with the
open-core approximation for the 4f states, and a simplified impurity
model for many-body modeling of the RIXS spectra.

L. Amidani, J. J. Joos, P. Glatzel, J. Kolorenc, arXiv:2310.18096,