Coherent phonons scattering by interstitial impurities in a quantum wire
Résumé
We investigate, in the harmonic approximation framework, the influence of interstitial defect on the scattering properties of elastic waves in quantum wire. The model is composed of two infinite atomic chains, assimilated to a perfect crystallographic waveguide, containing interstitial impurities. The problem is treated numerically using the matching method based on the Landauer-Büttiker principle. Considering the scattering boundary conditions as well as the conditions of symmetry, we study first the reticular dynamics of the perfect lattice witch consists, essentially, to determine the vibrating eigenmodes (propagating and evanescent modes) and their corresponding polarizations. The defect region, incorporated later in the waveguide, allows one to establish the mathematical formalism necessary to the diffusion. Numerical results show that the presence of defect in a quantum wire modifies particularly its mechanical and vibrational properties by the creation of new localized states and by bulk and surface phonons scattering. Its influence results in a general decrease of the transmission probability amplitude accentuated by Fabry-Pérot oscillations (interferences between reflected waves in the perturbed region) and/or Fano-like resonances (coherent coupling between propagating modes and localized-defect states). The transmission spectra, obtained by scattering experiments, can thus be regarded as fingerprints of the specific defect structure.
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