Re-examination of electronic structure of dilute Kondo transition-metal ions substituted into a Heavy Fermion compound
Correlations between the localized and conductive spins/charges have been the central issue of various fascinating quantum phenomena found on itinerant electron systems. Here, the obvious multiplet structures are presented on the Mn 2$p$ to 3$d$ x-ray absorption for a heavy fermion $\alpha$-(Yb,Lu)(Al$_{1-x}$Mn$_x$)B$_4$, indicating that the unoccupied electronic structure of the Mn site is described as the correlated high-spin 2+, even though magnetic measurements show the Mn sites to be nonmagnetic. This apparently paradoxical result demonstrates that a ligand field can effectively appear between localized Mn 3$d$ and surrounding B 2$p$ orbitals, which has been anticipated as a manifestation of a Kondo effect but not been clearly confirmed for most itinerant metals in spectroscopy. By contrast, the Mn 2$p$ photoemission indicates that the occupied Mn$^{2+}$ 3$d$ electrons still exhibit itinerant and nonlocally screened nature also owing to the Kondo-like correlation with the conductive B 2$p$, and heavier Yb 4$f$ and 5$d$ bands below the Fermi energy. The asymmetry on the particle-hole stimulates a reconsideration of the correlation and screening effects in the core-level spectroscopies.