Angle-resolved soft x-ray spectroscopy study of the electronic states of single-crystal MgB2

Angle-resolved soft x-ray measurements made at the boron K edge in single-crystal MgB 2 provide insights into the B 2p local partial density of both unoccupied and occupied band states. The strong variation of absorption with incident angle of exciting x rays permits the clear separation of contributions from σ states in the boron plane and π states normal to the plane. A careful comparison with theory accurately determines the energy of selected critical k points in the conduction band. Resonant inelastic x-ray emission at an incident angle of 15° shows a large enhancement of the emission spectra within about 0.5 eV of the Fermi level that is absent at 45° and is much reduced at 60°. We conclude that momentum transferred from the resonant inelastic x-ray scattering process couples empty and filled states across the Fermi level.