Photoemission measurements of the quasiparticle band of Na

Abstract
In this work, we calculate for Na the photoemission spectra at photon energy ∼18 eV and, then, compare them with the ‘‘absolute’’ measurement made by Lyo and Plummer. We find that, quite contrary to the conventional belief, only about half of the observed bandwidth reduction (∼0.6 eV) is caused by the self-energy correction. The remaining reduction is due to the surface-induced, momentum-nonconserving excitations and the broadening of quasiparticle states—these effects are intrinsic to photoemission. It is suggested that better band measurements should be done at higher photon energies, e.g., at about 70 eV for Na.

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