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DDC: 530 × Subject: ellipsometry ×

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    Dielectric function decomposition by dipole interaction distribution: Application to triclinic K2Cr2O7
    ([London] : IOP, 2020) Sturm, C.; Höfer, S.; Hingerl, K.; Mayerhöfe, T.G.; Grundmann, M.
    Here we present a general approach for the description for the frequency dependent dielectric tensor coefficients for optically anisotropic materials. Based on symmetry arguments we show that the components of the dielectric tensor are in general not independent of each other. For each excitation there exists an eigensystem, where its contribution to the dielectric tensor can be described by a diagonal susceptibility tensor. From the orientation of the eigensystem and the relative magnitude of the tensor elements, the dipole interaction distribution in real space can be deduced. In the limiting cases, the oriented dipole approach as well as the tensor of isotropic and uniaxial materials are obtained. The application of this model is demonstrated exemplarily on triclinic K2Cr2O7 and the orientation and directional distribution of the corresponding dipole moments in real space are determined. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
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    Optical properties of In2O3 from experiment and first-principles theory: influence of lattice screening
    ([Bad Honnef] : Dt. Physikalische Ges., 2018) Schleife, André; Neumann, Maciej D.; Esser, Norbert; Galazka, Zbigniew; Gottwald, Alexander; Nixdorf, Jakob; Goldhahn, Rüdiger; Feneberg, Martin
    The framework of many-body perturbation theory led to deep insight into electronic structure and optical properties of diverse systems and, in particular, many semiconductors. It relies on an accurate approximation of the screened Coulomb electron–electron interaction W, that in current implementations is usually achieved by describing electronic interband transitions. However, our results for several oxide semiconductors indicate that for polar materials it is necessary to also account for lattice contributions to dielectric screening. To clarify this question in this work, we combine highly accurate experimentation and cutting-edge theoretical spectroscopy to elucidate the interplay of quasiparticle and excitonic effects for cubic bixbyite In2O3 across an unprecedentedly large photon energy range. We then show that the agreement between experiment and theory is excellent and, thus, validate that the physics of quasiparticle and excitonic effects is described accurately by these first-principles techniques, except for the immediate vicinity of the absorption onset. Finally, our combination of experimental and computational data clearly establishes the need for including a lattice contribution to dielectric screening in the screened electron–electron interaction, in order to improve the description of excitonic effects near the absorption edge.