  Undoped and slightly Eu-doped SmB6 show the opening of a gap with decreasing
temperature below ~150 K. The spectral shapes near the Fermi level (EF) at 15 K
have shown strong increase in intensity of a peak at a binding energy (EB) of
around 12 meV with decreasing the photon energy (hn) from 17 eV down to 7 eV.
Angle resolved spectra of SmB6 measured at hn = 35 eV just after the in-situ
cleavage showed clear dispersions of several bands in the EB region from EF to
4 eV. Spin-polarized photoelectron spectra were then measured at 12 K and light
incidence angle of ~50 deg. In contrast to the lack of spin polarization for
the linearly polarized light excitation, clear spin polarization was observed
in the case of circularly polarized light excitation. The two prominent peaks
at EB~12 and ~150 meV have shown opposite signs of spin polarization which are
reversed when the helicity of the light is reversed. The sign and the magnitude
of spin- polarization are consistent with a theoretical prediction for the
6H5/2 and 6H7/2 states.
