Soft X-ray photoemission study of CeRhAs and related compounds: observation of a bulk pseudo-gap

We report bulk 4f and non-4f spectral functions near the Fermi level (EF) of a Kondo semiconductor CeRhAs and its related compound CePdSn by virtue of high-resolution soft X-ray photoemission. The non-4f spectrum of CeRhAs measured at 20K shows a shoulder at the binding energy of ∼0.18eV and almost negligible spectral weight at EF. Although a peak similar to a tail of the Kondo resonance is observed in the 4f spectrum of CeRhAs, the intensity at EF is suppressed compared with those of metallic Ce compounds. These facts are attributed to signatures of the formation of a pseudo-gap in CeRhAs