Anomalous Duality Of 4f Electrons In Filled Skutterudite Ceos4sb12

We study the electronic structure of the filled skutterudite CeOs4Sb12 using photoemission spectroscopy (PES). Soft x-ray excited Ce 3d-4f resonant PES confirms the existence of Ce 4f states at the Fermi level (E-F). Temperature dependent high-resolution laser-PES spectra reveal a pseudogap formation around E-F, which can be explained in terms of the hybridization gap. Simultaneously, a sharp feature is formed just above E-F with decreasing temperature. The heavy-fermion-like specific heat is attributed to the occupation of this feature. The results identify the origin of the anomalous coexistence of heavy-fermion and pseudogap behavior in terms of a symmetry dependent hybridization.