Observation of bulk electronic states of Kondo semiconductor YbB 12 by high-resolution soft X-ray photoemission spectroscopy

Abstract

Bulk valence band photoemission spectra of the Kondo semiconductor YbB 12 were measured with use of soft X-ray ( h ν = 700 eV) at 20 and 200 K and the Kondo resonance behavior was confirmed. Sharp bulk Yb 2+ 4f peaks are observed in the vicinity of Fermi level on fractured single crystals. From the spectra is estimated the Yb mean valence as 2.86 ± 0.01 at 20 K and 2.91 ± 0.01 at 200 K. The whole peaks of the Yb 3+ 4f multiplets are found to shift by ∼ 30 meV toward higher binding energies with decreasing the temperature from 200 to 20 K. On the other hand, the shift of the peak energy position of the Yb 2+ 4f spectra toward lower binding energies with decreasing the temperature is found to be less than 10 meV. The temperature dependence of the Yb 4f photoemission spectra is well explained by the non-crossing approximation (NCA) calculation based on the single impurity Anderson model (SIAM).