Spin-Polarized Angle-Resolved Photoelectron Spectroscopy of the So-Predicted Kondo Topological Insulator SmB6

Undoped and slightly Eu-doped SmB6 samples show the opening of a gap with decreasing temperature below similar to 150 K. The spectral shapes near the Fermi level (E-F) at 15 K have shown a marked increase in intensity of the peak at a binding energy (E-B) of approximately 12 meV with decreasing photon energy (hv) from 17 to 7 eV. Angle-resolved spectra of SmB6 measured at hv = 35 eV just after the in situ cleavage showed clear dispersions of several bands in the E-B region from E-F to 4 eV. Spin-polarized photoelectron spectra were then measured at 12 K and a light incidence angle of similar to 50 degrees. 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 E-B similar to 3 12 and similar to 150 meV have shown opposite signs of spin polarization which are reversed when the helicity of the light is reversed. The sign and magnitude of spin polarization are consistent with a theoretical prediction for the H-6(5/2) and H-6(7/2) states.