Yamaguchi, J., Sekiyama, A., Kimura, M. Y., Sugiyama, H., Tomida, Y., Funabashi, G., Kimori, S., Balashov, T., Wulfhekel, W., Ito, T., Kimura, S., Higashiya, A., Tamasaku, K., Yabashi, M., Ishikawa, T., Yeo, S., Lee, S.-I., Iga, F., Takabatake, T., Suga, S.

Different evolution of the intrinsic gap in strongly correlated SmB

_{6}in contrast to YbB

_{12}

New Journal of Physics

**15**, (4),pp 043042/1-12 (2013)

Dependence of the spectral functions near the Fermi level on temperature and rare-earth atom doping was studied in detail for strongly correlated alloys Sm

_{1−x}Eu_{x}B_{6}and Yb_{1−x}Lu_{x}B_{12}by photoelectron spectroscopy at ≈ 8000 eV as well as at 7 and 8.4 eV. It was found that the 4f lattice coherence and intrinsic gap are robust for Sm_{1−x}Eu_{x}B_{6}at least up to the Eu substitution of x = 0.15 while both collapse by Lu substitution already at x = 0.125 for Yb_{1−x}Lu_{x}B_{12}. As for the temperature dependence of the spectral shapes near the Fermi level at low temperatures, rather contrasting results were observed between YbB_{12}and SmB_{6}. Although the gap shape does not change below 15 K for YbB_{12}with the characteristic temperature T* of 80 K, the spectral shape of SmB_{6}with a T* of 140 K shows that the peak beyond the gap is further increased below 15 K. The temperature dependence of the spectra near the intrinsic gap is clearly different between SmB_{6}and YbB_{12}, although both materials have so far been categorized in the same kind of strongly correlated semiconductor. The possibility of the surface contribution is discussed for SmB_{6}.