Bloch k-selective resonant inelastic scattering of hard x rays at valence electrons of Ni in NiAl

We have measured x-ray fluorescence spectra from a stoichiometric NiAl sing le crystal after resonant excitation at the Ni K edge using synchrotron rad iation. The shape of the spectra strongly depends on both excitation energy and scattering angle. This effect can be understood by considering a reson ant inelastic-scattering process leading to a law of Bloch k-momentum conse rvation. We find clear evidence of this Bloch k-selection rule in the hard x-ray region. The measured spectra an in good agreement with calculated spe ctra based on a linearized augmented plane wave band-structure calculation.