Positron surface states bound by the Newns-Barton potential

Abstract

The binding energies and eigenfunctions of the surface states of positrons outside materials with negative positron affinity are considered. When the material is represented by a continuum hydrodynamic model with finite dispersion the potential takes the Newns-Barton form. The characteristic material parameter is B = ω p/ β where ω p is the bulk plasma frequency and β ≅ √ 3 5 x the Fermi velocity. For aluminium B ≅ 0.6 a −1 (a is the Bohr radius) and the Newns-Barton potential yields a ground state binding energy E (1) ≅ 0.46 ev - considerably smaller than the binding energy of the pure image (or non dispersive) potential for which E (1) ≅ 0.85 ev.