A comparative study of the electronic and optical properties of Mn-Bi-Te layered compounds was carried out using spectroscopic ellipsometry (SE) over a photon energy range of 0.7–6.5 eV at room temperature and density functional theory (DFT)-based first-principle calculations within the general gradient approximation with Hubbard like correction (GGA+U) and allowance for a spin-orbital coupling. The total energies of the above compounds in ferromagnetic (FM) and antiferromagnetic (AFM) spin configurations are obtained by taking the long-range van der Waals interaction into account. The stability of the AFM state of MnBi2Te4 and MnBi4Te7 over the corresponding FM counterpart is disclosed. The SE-based and calculated dielectric functions are compared. It is shown that interband optical transitions in the accessed photon energy range mainly occur between Mn 3d + Te 5p states of the valence band and Bi 6p + Te 5p with a small admixture of Mn 3d states of the conduction band.

Boron doped Si/SiO2/substrate (Si:B) structure with subwavelength grating on the top Si:B layer was studied by spectroscopic ellipsometry and photoluminescence spectroscopy at room temperature. A clear modification of the dielectric function was observed after reactive ion etching of the top Si:B layer subjected to laser lithography to make a subwavelength grating with high precision. A striking feature of the dielectric function of the grated surface layer is a sharp and intense peak at the energy of 2.968 eV in the interband density of states. Emission band with a remarkable peak structure that emerges in the photoluminescence spectrum of the grated multilayer structure at and below the last energy is absent on pure or boron doped Si. The obtained results are discussed in terms of the G-doping effect in the considered surface grated multilayer structure.

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Narrow bandgap Bi2Se3, Bi2Te3, and Sb2Te3, commonly referred to as classic 3D topological insulators, were studied at room temperature by spectroscopic ellipsometry and optical reflection spectroscopy over the mid-IR–near-infrared photon energy range. Complementarily, Hall measurements were performed. Plasmons in optical loss function and reflection coefficient were identified. The conventional approach based on the high frequency dielectric constant was shown to work well in the description of plasmons in Bi2Se3 and Sb2Te3 and to fail in the case of a similar compound, Bi2Te3. The obtained results are discussed in terms of single- and multivalley approaches to the studied samples with taking the details of the calculated band structure into account.

bly because of the obvious difficulties in the preparation of MnBi 2 Te 4 • n(Bi 2 Te 3 ) with high index n and unavailability of samples.We have succeeded in this regard and present here the crystal structure of the members with n = 4, 5, and 6, summarize all available structural data for MnBi 2 Te 4 • n(Bi 2 Te 3 ), trace the evolution of Raman spectra of MnBi 2 Te 4 • n(Bi 2 Te 3 ) that embraces all n from 0 to 6 as well as n = ∞ (Bi 2 Te 3 ), and provide a thorough analysis of the obtained Raman data. II. SYNTHESIS AND CRYSTAL STRUCTUREOF MnBi 2 Te 4 • n(Bi 2 Te 3 )A. Synthesis and crystal growth