Photoemission study of the skutterudite compounds CoSb₃ and RhSb₃

We have studied the electronic structure of the skutterudite compounds CoSb₃ and Co(Sb_0.96Te_0.04)₃ by photoemission spectroscopy. Valence-band spectra revealed that a significant amount Sb 5p states are present near the Fermi level and are hybridized with Co 3d states just below it. The spectra are well reproduced by the band-structure calculation, suggesting that the effect of electron correlations is not important. When Te is substituted for Sb and n-type carriers are doped into CoSb₃, the spectra are shifted to higher binding energies as described by the rigid-band model. From this shift and the free-electron model for the conduction and valence bands, we have estimated the band gap of CoSb₃ to be 0.03-0.04eV, consistent with transport measurements. Photoemission spectra of RhSb₃ have also been measured and revealed expected similarities to and differences from those of CoSb₃. Unusual temperature dependence has been observed for the spectra of CoSb ₃ and RhSb₃ in the vicinity of the Fermi level.