Possible Kondo resonance in PrFe4P12 studied by bulk-sensitive photoemission

Pr $4f$ electronic states in Pr-based filled skutterudites $\text{Pr}{T}_{4}{X}_{12}$ ($T=\text{Fe}$ and Ru; $X=\mathrm{P}$ and Sb) have been studied by high-resolution bulk-sensitive Pr $3d\ensuremath{\rightarrow}4f$ resonance photoemission. A very strong spectral intensity is observed just below the Fermi level in the heavy-fermion system ${\text{PrFe}}_{4}{\mathrm{P}}_{12}$. The increase of its intensity at lower temperatures is observed. We speculate that this is the Kondo resonance of Pr, the origin of which is attributed to the strong hybridization between the Pr $4f$ and the conduction electrons.