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Soft x-ray energy-dependent angle-resolved photoemission measurements are performed on the heavy-fermion superconductor CeIrIn5 to study the Fermi surface (FS) and the electronic structure near the Fermi level in the ΓMZA plane. The non-dispersive band designated as the Ce 4f7/21 final state is found at 280 meV along with the main body of the valence band consisting of highly dispersive In 5p bands, which are in good qualitative agreement with the band structure calculation based on the itinerant 4f electron model. Furthermore, we found two electron-like and one hole-like cylindrical FSs at the M (A) and Γ (Z) points. The Fermi momenta of the observed FSs are consistent with the de Haas–van Alphen experiment, while they contradict the stronger anisotropy of the FS along the kz direction predicted by the band calculation. The results suggest stronger two-dimensionality of the electronic structure of CeIrIn5 and point to the need for its theoretical verification.

CeOs(4)Sb(12) and CeFe(4)P(12) are classified as Kondo semiconductors, which show coupled changes in electrical transport, thermodynamic and magnetic properties with a low-temperature semiconductor-like electrical resistivity. We have carried out core level and valence band photoemission spectroscopy on single crystal CeOs(4)Sb(12) and CeFe(4)P(12) to study their electronic structure and the evolution of states at the Fermi level as a function of temperature (∼10-300 K). The Ce 3d core level spectra show the presence of f(0), f(1) and f(2) final states with very different relative intensities in the two compounds. Single-impurity Anderson model calculations provide f electron counts of n(f) = 0.97 and 0.86 per Ce atom, suggestive of a low- and high-T(K) (= single ion Kondo temperature) for CeOs(4)Sb(12) and CeFe(4)P(12), respectively. The high-resolution temperature-dependent near-Fermi level spectra show pseudogaps of energy ∼ 50 meV and ∼ 110 meV in the valence band density of states (DOS) of CeOs(4)Sb(12) and CeFe(4)P(12), respectively. The temperature dependence of the DOS at the Fermi level follows the change in effective magnetic moment estimated from magnetic susceptibility for both materials, confirming the Kondo nature of the pseudogap in CeOs(4)Sb(12) and CeFe(4)P(12). A compilation of measured pseudogaps using photoemission and optical spectroscopy identifies the charge gaps Δ(C) for Ce-based Kondo semiconductors and provides a direct relation with T(K) given by Δ(C) ∼ 2k(B)T(K). In conjunction with the known behaviour of the spin gaps Δ(S) ∼ k(B)T(K), the results establish the coupled energy scaling of the spin and charge gaps in Kondo semiconductors.