Positron-induced emission of electron–positron pairs from solid surfaces

• Published in: Journal of physics. Condensed matter Vol. 21; no. 35; pp. 355002 - 355002 (12)
• Main Authors: Giebels, F, Gollisch, H, Feder, R
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 02.09.2009; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states; Exact sciences and technology; Physics; Positron states; Pair correlation function; Quasiparticles; Valence electron; Density functional method; Angular distribution; Electron-positron interactions; Copper; Positron states; Matrix elements; Coulomb interaction
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/21/35/355002

The collision of a low-energy positron, which impinges on a crystalline surface, with a valence electron may result in the emission of a spatially separated time-correlated electron-positron pair. We present a method for calculating the cross section for this positron surface reaction channel, which we briefly refer to as (p, ep) in analogy to electron-induced pair emission (e, 2e). The two-particle final state is represented by a product of an electron and a positron diffraction state coupled by a 'correlation factor', which accounts for the screened Coulomb interaction. The electron-solid and positron-solid quasi-particle potentials are based on first-principles calculations within density functional theory. Numerical (p, ep) results are presented for Cu(111) and compared to their (e, 2e) counterparts. Energy distributions for constant emission angles reflect, to a large extent, the valence electron density of states. In equal-energy (p, ep) angular distributions, the Coulomb interaction produces a central accumulation zone-in contrast to a depletion zone for (e, 2e)-the relative weight and the extension of which are subject to 'matrix element effects'. At larger angles sharp features arise from single-particle surface resonances.