Coordinate-Invariant Lyddane-Sachs-Teller Relationship for Polar Vibrations in Materials with Monoclinic and Triclinic Crystal Systems

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic β-Ga 2 O 3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

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“…(3) satisfies the KramersKronig integral condition [23,37,51] and which can be set as additional side condition during the CP-MDF analysis.…”

Section: Higher Energy Band-to-band Transitionsmentioning

confidence: 99%

“…Schubert et al [23,37] adapted the concept of the dielectric eigendisplacement polarizations in the Born and Huang model [38] to develop a monoclinic CP-MDF for phonon excitations in β-Ga 2 O 3 . Sturm et al [8] provided a CP analysis for β-Ga 2 O 3 extending the Born and Huang model [38] to interband excitations.…”

Section: Introductionmentioning

confidence: 99%

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β−Ga2O3

et al. 2017

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“…Through refraction and diffraction, which depend on the thicknesses and refractive indexes of the layers, the light wavelengths that will be reflected with higher intensities are selected, generating the displayed colors. As shown above (see disordered materials [23][24][25] but its application for the present case, chitin with a varying concentration of melanin, is not straightforward. In any case, there is a direct relation between the refractive indexes and the measured relative permittivity.…”

Section: The Structural Colormentioning

confidence: 90%

Mapping the local dielectric constant of a bio‑nanostructured system

Valeriano¹,

Andrade²,

Vasco³

et al. 2020

Preprint

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The aim of this work is to determine the dielectric constant value of a bio-nanostructured system via Electrostatic Force Microscopy (EFM) and to show how this method is useful to study natural photonic crystals. We mapped the dielectric constant of the cross-section of the posterior wing of the damselfly Chalcopteryx rutilans with nanometric resolution and obtained not only structural information on its constitutive nanolayers but also on the absolute values of the dielectric constant variation in a nanometric scale. By relating the measured profile of the static dielectric constant to the profile of the refractive index in the visible range, combined with optical reflectance measurements and simulation, we were able to describe the origin of the strongly iridescent wing colors of this Amazonian rainforest damselfly. The method we demonstrate here should be useful for the study of other nanostructured biological systems.

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“…For the phonon modes also the (relative) oscillator strengths are well reproduced by theory. We note that a modified Lyddane–Sachs–Teller relation for monoclinic and triclinic materials has been proposed.…”

Section: Dielectric Functionmentioning

confidence: 92%

Optically anisotropic media: New approaches to the dielectric function, singular axes, microcavity modes and Raman scattering intensities

Grundmann

Sturm

Kranert

et al. 2016

Physica Rapid Research Ltrs

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Six out of seven crystal systems are optically anisotropic and birefringent. We review recent insight that biaxial crystals generally exhibit four singular axes (or exceptional points) which can pairwise degenerate for special cases. Planar anisotropic microcavities are discussed as effectively biaxial systems and we predict exceptional points and demonstrate experimentally partially coalesced eigenstates. Also the general form of the dielectric function of anisotropic crystals based on individual dipole oscillators for phonon and electronic resonance is discussed. The impact of birefringence on Raman scattering intensities has been historically either ignored or modeled incorrectly. A recent theory for uniaxial and biaxial crystals explains experimental Raman scattering intensities for excitation off the principal directions without free parameters, allowing the unambiguous determination of the Raman tensor components. The above points are demonstrated and relevant in particular for the currently technologically important materials GaN, ZnO (uniaxial) and β‐Ga2O3 (biaxial).

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Coordinate-Invariant Lyddane-Sachs-Teller Relationship for Polar Vibrations in Materials with Monoclinic and Triclinic Crystal Systems

Cited by 32 publications

References 32 publications

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β−Ga2O3

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β−Ga2O3

Mapping the local dielectric constant of a bio‑nanostructured system

Optically anisotropic media: New approaches to the dielectric function, singular axes, microcavity modes and Raman scattering intensities

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