Analysis of Possible Scattering Processes for Bloch Positronium in Ionic Crystals at Elevated Temperatures

Abstract

T he role of non polar optic phonon scatterin g an d of umklapp acoustic phonon scattering is analy zed for a delo cali zed p ositroni um atom in ionic crystals at elev ated temp eratures. A t temp eratures above w hich they become essential both of these scattering mechanisms contribute to the imagina ry self-energy of p ositroni um renormalizi ng its acoustic def ormation potential constant. I t w as such a renormalizati on that w as recently observed exp erimentally for delo cali zed positroni um in Mg F 2 crystal. W e put forw ard the theoretical explanati on of these exp eriments based up on the mo del of nonp olar optic phonon scattering of positroniu m. A n e˜ect analogous to that observed in MgF 2 is predicted for crystalli ne quartz ab ove the temp erature of (˜À Ù )-phase transitio n.