Polariton local states in impure crystals.
Item
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Title
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Polariton local states in impure crystals.
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Identifier
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AAI9830753
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identifier
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9830753
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Creator
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Podolsky, Victor Semenovich.
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Contributor
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Adviser: Alexander Lisyansky
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Physics, Optics | Engineering, Materials Science
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Abstract
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We consider phonon-polariton local states in impure ionic crystals. Taking into account the defect-induced variations of the elastic constants, we found several local states of different symmetry. These states arise in the polariton gap for an infinitesimally small value of impurity strength, and they are predominated by long-wavelength modes. It is caused by the singularity in the density of the polariton states, which is generic for any isotropic dipole-active phonon mode with a negative dispersion. The crystal anisotropy removes this singularity and sets a finite threshold for local states. We investigate a crossover between polariton and phonon local states. We show that, due to a disproportion between the phonon and photon group velocities in 3D systems, the crossover takes place in a narrow spectral interval near the bottom of the gap, and the phonon content of the local states dominates over their photon content. To eliminate this disproportion, we place the active medium inside a narrow waveguide. We show that a coherent interaction between the waveguide modes and the polarization waves in an atomically thin dielectric layer (ionic 2D-crystal), gives rise to new excitations--2D-polaritons. The features of their spectra and the structure of the defect-induced polariton local state depend on the waveguide width. When the width becomes comparable with the localization radius, 2D-polariton local state transforms into localized waveguide mode. Our estimates show that, in the sub-micron waveguides, the localized mode can be provided by a single impurity or a local structural defect.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
