Many-Body Effects Observed in the Positron Annihilation Experiment

The flrst question considered in the paper is connected with the electronipositron interaction in real metals. It is shown that the Bloch modifled ladder (BML) theory [1], in contrast to all other approaches, is able to describe (at least qualitatively) experimental e{p momentum densities for both simple and transition metals. Such a flnding is important because all these theories, except BML, ignore the in∞uence of the lattice potential on the e{p interaction, concerning both intraband and interband transitions. The next subject of the paper are the electron{electron correlations which should, in principle, be also observed in the positron annihilation experiments. However, Carbotte and Kahana [2] showed that (at least for positrons in jellium) the dynamical parts of the e{p and e{e correlation cancel each other. Consequently, the remaining many-body efiects come only from the static part of these interactions. Because the static e{e correlations are (at least approximately) included