1 0 Ju l 2 00 1 ARPES Study of X - Point Band Overlaps in LaB 6 and SmB 6 – Contrast to SrB 6 and EuB 6
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چکیده
In contrast to our recent finding of an X-point band gap in divalent hexaborides, we report here that angle resolved photoemission spectroscopy (ARPES) data shows that the gap is absent for trivalent LaB 6 and is absent or nearly so for mixed valent SmB 6. This finding demonstrates a nontrivial evolution of the band structure from divalent to trivalent hexaborides. Rare earth hexaborides continue to challenge condensed matter physicists to explain their exotic properties, e.g., the weak high temperature ferromag-netism in lightly doped or nominally stoichiometric divalent hexaborides [1]. An important issue is the existence or the absence of band overlap at the X point of the cubic Brillouin zone appropriate for these materials. Such an overlap is predicted by band calculations and would render divalent hexaborides to be semi-metallic conductors, whereas they would be insulators if there is an X-point gap. Recent angle resolved photoemission spectroscopy (ARPES)
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