Angle-resolved photo-emission spectroscopy was used to study the complete absence of an X-point band gap for trivalent LaB6. An X-point band gap was found in divalent hexaborides. The two findings implied a non-trivial evolution of the band structure from divalent to trivalent hexaborides.

ARPES Study of X-Point Band Overlaps in LaB6 and SmB6 - Contrast to SrB6 and EuB6. Mo, S.K., Gweon, G.H., Denlinger, J.D., Kim, H.D., Allen, J.W., Olson, C.G., Höchst, H., Sarrao, J.L., Fisk, Z.: Physica B, 2002, 312-313, 668-9