Optical Conductivity of CeNiSn, CeRhSb, and CeRhAs

Abstract

The optical reflectivity spectra of the Kondo semiconductors CeNiSn, CeRhSb, and CeRhAs have been measured in a wide photon energy range to obtain the optical conductivity spectra σ(ω). For CeNiSn and CeRhSb, two pronounced peaks in the mid-infrared (IR) region and small pseudogaps in the far-IR region were observed at low temperatures ( T ). The two peaks are attributed to optical transitions related with the two bands arising from the spin–orbit splitting of Ce 4 f . For CeRhAs, σ(ω) exhibits a gap which develops gradually with cooling. The observed (pseudo)gap widths and T dependent variations are largest for CeRhAs and smallest for CeNiSn, well corresponding to their Kondo temperatures. For CeNiSn and CeRhSb, the T dependence of σ(ω) in the far-IR suggests the formation of a narrow Drude peak caused by a c – f mixing. The results may indicate that the pseudogap is opened in a heavy quasiparticle band.