Interpretation of positron-annihilation data with respect to the electron-positron enhancement factors. I. Theory.

Abstract

The influence of the positron distribution and electron-positron interactions on the momentum density \ensuremath{\rho}(p) of annihilation quanta in real metals is discussed on mathematical grounds. We show that in simple metals, neither the assumed form of the positron wave function nor state-independent electron-positron correlations can change appreciably the shape of \ensuremath{\rho}(p) inside the central Fermi surface. The role of momentum dependence of two-particle correlations is set forth. For localized electronic populations, this property does not occur: both the form of the positron distribution and the locality of correlation effects have a crucial influence on the resulting momentum density \ensuremath{\rho}(p). The same features have the umklapp components for delocalized electrons.