ARPES study of X-point band overlaps in LaB6 and SmB6 — contrast to SrB6 and EuB6

Abstract In contrast to our recent finding of an X-point band gap in divalent hexaborides, we report here that angle resolved photoemission spectroscopy data show that the gap is absent for trivalent LaB6 and is absent or nearly so for mixed valent SmB6. This finding demonstrates a nontrivial evolution of the band structure from divalent to trivalent hexaborides.