Kondo scaling of the pseudogap inCeOs4Sb12 andCeFe4P12

Abstract

CeOs4Sb12 and CeFe4P12 are classified as Kondo semiconductors, which show coupled changesin electrical transport, thermodynamic and magnetic properties with alow-temperature semiconductor-like electrical resistivity. We have carried outcore level and valence band photoemission spectroscopy on single crystalCeOs4Sb12 andCeFe4P12 tostudy 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 off0,f1 andf2 final states with very different relative intensities in the two compounds.Single-impurity Anderson model calculations provide f electron counts ofnf = 0.97 and 0.86 per Ce atom, suggestive of a low- and high-TK (= single ion Kondotemperature) for CeOs4Sb12 and CeFe4P12, respectively. The high-resolution temperature-dependent near-Fermi level spectra show pseudogaps ofenergy ∼ 50 meV and ∼ 110 meV in the valence band density of states (DOS) ofCeOs4Sb12 andCeFe4P12, respectively. The temperature dependence of the DOS at the Fermi levelfollows the change in effective magnetic moment estimated from magneticsusceptibility for both materials, confirming the Kondo nature of the pseudogap inCeOs4Sb12 andCeFe4P12. Acompilation of measured pseudogaps using photoemission and optical spectroscopy identifies the chargegaps ΔC for Ce-based Kondo semiconductors and provides a direct relation withTK givenby ΔC ∼ 2kBTK. In conjunction with the known behaviour of the spin gapsΔS ∼ kBTK, the results establish the coupled energy scaling of the spin and charge gaps in Kondosemiconductors.