Angle-resolved soft x-ray spectroscopy study of the electronic states of single-crystalMgB2

Abstract

Angle-resolved soft x-ray measurements made at the boron K edge in single-crystal ${\mathrm{MgB}}_{2}$ 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 $\ensuremath{\sigma}$ states in the boron plane and $\ensuremath{\pi}$ 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\ifmmode^\circ\else\textdegree\fi{} shows a large enhancement of the emission spectra within about 0.5 eV of the Fermi level that is absent at 45\ifmmode^\circ\else\textdegree\fi{} and is much reduced at 60\ifmmode^\circ\else\textdegree\fi{}. We conclude that momentum transferred from the resonant inelastic x-ray scattering process couples empty and filled states across the Fermi level.