Electronic structure and the valence state of Yb2Pd2Sn and YbPd2Sn studied by photoelectron and resonant x-ray emission spectroscopies

We have examined the electronic structure of the heavy fermion Yb2Pd2Sn in comparison with the superconductor YbPd2Sn by means of high-resolution photoelectron spectroscopy (PES) and resonant x-ray emission spectroscopy (RXES). The PES data are interpreted in light of the density of states calculated within the local density approximation plus the dynamical mean-field theory. Our analysis of the RXES data shows that the valence of Yb in Yb2Pd2Sn is weakly fluctuating, indicating weak but finite c-f hybridization, and decreases slightly with temperature. In contrast, the Yb valence in YbPd2Sn is nearly 3+ and does not show any temperature dependence, suggesting that the Yb 4f electrons are localized and the superconductivity is due to the Pd conduction electrons. The constant initial state spectra at the Yb 4d-4f resonance for Yb2Pd2Sn clearly show resonant behavior for Yb3+ and antiresonance for Yb2+, indicating that the Yb3+ and Yb2+ states are intimately correlated