Energy dependence of experimental Be Compton profiles

Abstract

High-resolution Compton scattering measurements on Be single crystals along three main crystallographic directions ([10\ensuremath{\cdot}0], [11\ensuremath{\cdot}0], and [00\ensuremath{\cdot}1]) have been carried out using incident photon energies of 10, 29, and 56 keV to study the energy dependence of the scattering cross section. The experimental Compton profiles are in good agreement with theoretical profiles employing the local density approximation--based band theory framework. Extensive comparisons between the computed and measured profiles, their first derivatives, and anisotropies defined as differences between various pairs of profiles show an excellent level of accord. The details related to the Fermi surface are clearly seen in the experimental Compton profiles. However, subtle but systematic direction-dependent discrepancies remain between the experimental and theoretical profiles, suggesting that a better treatment of electron correlation effects in the inhomogeneous electron gas is needed to develop a satisfactory description of the momentum density in Be. Our analysis also indicates that the effective momentum resolution in low-energy Compton experiments possesses intrinsic limitations due to final-state interactions and possibly cannot be enhanced arbitrarily by improving the instrumental resolution.