Surface state and resonance effects in electron-pair emission from Cu(111)

Abstract

We report on an electron-pair emission study from a Cu(111) surface excited by electron impact with different primary electron energies. We identify in the energy spectra, features that can be directly related to the underlying band structure. This, in turn, proves an important assumption in the theoretical description of the pair-emission process, namely that an effective single-particle picture for the electronic structure is an adequate description. With this observation, it is possible to identify the orbital character of the participating valence state. The relative pair-emission intensity from the surface state and 3d states is observed to vary dramatically with the primary energy. We observe particular conditions where the contribution from the Shockley surface state is strong. We propose a simplified model to explain this observation.

Positron-electron pairs emitted from metallic and oxide surfaces

“…Several electron beam evaporators are available for the deposition of metal and oxide films. The coincidence spectrometer has been explained in more detail elsewhere [17]. The key components are a pair of hemispherical analyzers with 200 mm mean radius, which we call "left" and "right" respectively.…”

“…This makes it possible to compute the arrival time histogram dt = t left − t right and this will show a peak residing on a constant background. The temporal width of the peak can be understood by electron-optical considerations of the actual spectrometer [17][18][19]. Following standard procedures it is possible to remove the aggregate effect of the "random" coincidences [17,20,21].…”

Exact time evolution of the pair distribution function for an entangled two-electron initial state

“…As an outlook, we speculate that our theoretical findings could be important in several problems with the initial confinement of interacting (repulsively or attractively) particles, like in ionization problems of atoms [28,29] with transient atomic structures or in electron-hole and electron-electron dynamical processes [30,31] in condensed matter physics. The sign effect of interparticle interaction can result in peculiarities beyond a simple mean-field description applied commonly for charge-neutral [30] pair excitations in metals.…”

“…Similarly, the interpretation of data obtained in electron-pair emission spectroscopy needs methods beyond an effective one-electron treatment. Indeed, it was emphasized [31] that the very existence of correlation cannot be formulated within a single-particle picture.…”

Energy Relations of Positron-Electron Pairs Emitted from Surfaces

“…The details of the coincidence spectrometer can be found elsewhere [10,17,18]. It consists of two hemispherical electron energy analyzers with transfer lenses and angular acceptance AE15°.…”