Bulk Band Gaps in Divalent Hexaborides

Abstract

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB_6 additionally provide a stringent test case for proper inclusion of many-body effects in quasi-particle band calculations.

4 pages, 3 figures; new RIXS analysis; accepted for publication in PRL

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• Excitonic instability in two-dimensional degenerate semimetals
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• Kondo and anti-Kondo coupling to local moments in EuB${}_6$
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• Revelation of the role of impurities and conduction electron density in the high resolution photoemission study of ferromagnetic hexaborides
• Time-reversal symmetry breaking driven topological phase transition in EuB${}_6$
• Electronic Structure of Calcium Hexaboride within the Weighted Density Approximation
• Electronic transport in EuB${}_6$
• Double Exchange Model for Magnetic Hexaborides
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• Optical spectroscopy study on the electronic structure of $E{u}_{1-x}C{a}_x{B}_6$
• ARPES insights on the metallic states of YbB6(001): E(k) dispersion, temporal changes and spatial variation
• Theory of Excitonic States in CaB6
• Possible quantum nematic in a colossal magnetoresistance material
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• Quantum chemical insights into hexaboride electronic structures: correlations within the boron $p$-orbital subsystem
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