Optical Observation of Energy Gap of R₃Au₃Sb₄ (R=La, Ce)

Abstract

Reflectivity spectra of R₃Au₃Sb₄ (R=La, Ce) polycrystals were measured in the photon energy range from 5 meV to 40 eV at 6, 78 and 297 K. A narrow energy gap was observed for both materials. In La₃Au₃Sb₄, it was seen that the energy gap of about 150 meV is an indirect one. The absorption due to the direct and allowed transition was observed around 0.7 eV. These results are consistent with the calculated band structure. In Ce₃Au₃Sb₄, it was seen that the energy gap of about 70 meV is a direct one. The gap is considered to consist of the occupied 4f state and the unoccupied 5d state.