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Type: Artigo de periódico
Title: Theory Of A Zone-boundary Collective State In A1: A Model Calculation
Author: Sturm K.
Oliveira L.E.
Abstract: A two-band model, which previously was used successfully to evaluate the optical absorption in A1, is applied to derive the k- and -dependent dielectric function M(k,) for k parallel to the [100] direction with use of degenerate perturbation theory. Within the nearly-free-electron approximation, it is shown that a pair of (200) Bragg planes gives rise to another pole in the energy-loss function Im[-1] and hence to a collective mode. Both the dispersion of the mode throughout the first Brillouin zone and the strength of the mode are evaluated and are found to agree very well with electron-energy-loss spectroscopy data. A detailed discussion of the nature of this mode is given. The mode is of the same origin as the so-called zone-boundary collective state (ZBCS) first proposed by Foo and Hopfield in Na. Comparison is made with a numerical calculation of M(k,) by Singhal for some discrete k values. The general importance of the ZBCS for the understanding of the energy-loss spectrum and for more complicated systems is pointed out. © 1984 The American Physical Society.
Rights: aberto
Identifier DOI: 10.1103/PhysRevB.30.4351
Date Issue: 1984
Appears in Collections:Unicamp - Artigos e Outros Documentos

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