Bulk Band Gaps in Divalent Hexaborides: A Soft X-Ray Emission Study

Boron K-edge soft X-ray emission and absorption are used to address the fundamental question of whether divalent hexaborides are intrinsic semimetals or defect-doped band gap insulators. These bulk-sensitive measurements, complementary and consistent with surface-sensitive angle-resolved photoemission experiments, confirm the existence of a bulk band gap and the location of the chemical potential at the bottom of the conduction band.