Effect of Ps-phonon interaction on the momentum distribution of positronium atoms in a crystal

Abstract

In single crystals, posttronium can exist both in the localized and delocalized states [1–8]. Delocalized positronium is revealed by peaks in the angular distribution in the annihilation of γ quanta (AD), which occupy positions corresponding to the projections of the reciprocal lattice vectors onto a direction determined by the setup. The peaks indicated show the Bloch states of positronium [1–3]. As the temperature increases, the fraction of delocalized positronium decreases, while the peaks stemming from it broaden (see [3–7]). The broadening of the momentum distribution n(k) of positronium atoms (compared to the Maxwellian distribution with the particle mass equal to the rest mass (m_o) of the Ps atom), as shown by Ikary [9], viewing the Ps atom as an exciton, can be explained as the decay of quasiparticle positronium states due to the Ps-phonon interaction.