Energy dependence of quasiparticle damping at a metal surface

We evaluate the energy dependence of the imaginary part of the electron self-energy Im Sigma in the vicinity of a metal surface modeled with jellium via numerical calculations based on the GW approximation. When the electron is inside the surface, conventional quadratic scaling, IM Sigma similar or equal to(E-E-F)(2) for E-->E-F, holds for electron positions all the way to the jellium edge and for energies at least up to the vacuum level E-E-F similar or equal to 4 eV. However, when the electron is in the vacuum outside the surface, large departures from quadratic scaling are obtained for most energies for which it holds in the bulk. These departures grow as the electron-surface separation increases. This effect is traced to the suppression of one-electron decay channels near the Fermi level.