Electron momentum density in yttrium
  A simultaneous analysis of high-resolution directional Compton profiles and two-dimensional angular correlation of positron annihilation experimental data has been performed by studying both a directional anisotropy of measured spectra and reconstructed densities. The results were compared with theoretical fully-relativistic augmented plane-wave calculations with and without including correlation effects. Estimated symmetry selection rules have allowed us to establish some values of Fermi momenta. Both experiments show exactly the same shape of the anisotropy of the momentum densities, in agreement with the band structure results. In the positron annihilation data electron-positron correlations are not seen while in both experiments electron-electron correlations are observed. 
G. Kontrym-Sznajd, M. Samsel-Czekala, A. Pietraszko, H. Sormann, S.   Manninen, S. Huotari, K. Hamalainen, J. Laukkanen, R.N...