Three-dimensional electron momentum densities of solids

We report on the measurement of the three-dimensional electron momentum density (MM) of solids by means of the (gamma, ey) reaction. Fixing the reaction kinematics by a coincidence condition, the triple-differential cross section for Compton scattering is proportional to the EMD. The experiments were performed either at the wiggler beamline of the European Synchrotron Radiation Facility (ESRF) or the undulator beamline of the PETRA storage ring at Deutsches Elektronen-Synchrotron (DESY) with photon energies of about 150 keV. Experimental three-dimensional EMDs of graphite, fullerene and aluminium are compared with theoretical ones obtained from band-structure calculations like the full-potential linear muffin-tin orbital, augmented-planewave and pseudopotential formulations. In addition, the change of the EMD caused by alloy formation has been studied in the Cu-Ni system and the results are compared with the Korringa-Kohn-Rostoker coherent potential approximation.