  We present a study on the high-Tc superconductor (HTSC) YBa2Cu3O7-x (YBCO)
using polarization-dependent X-ray absorption and resonant inelastic X-ray
scattering. High-resolution measurements using synchrotron-radiation are
compared with calculations using a quasi-atomic multiplet approach performed at
the Cu 2p3/2-edge of YBCO. We use a multiplet approach within the single
impurity Anderson model to reproduce and understand the character of the
localized low-energy excitations in YBCO. We observe a distinct peak at about
0.5 eV in O K RIXS. This peak shows dependence on doping, incident energy, and
momentum transfer that suggests that it has a different origin than the
previously discussed cuprate bi-magnons. Therefore, we assign it to
multi-magnon excitations between the Zhang Rice bands and/or the Upper Hubbard
bands, respectively.
