Electronic structure and dielectric function of Mn-Bi-Te layered compounds

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 MnBiTe and MnBiTe 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.We acknowledge the support by the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02), Russian Foundation for Basic Research (Grant No. 18-52-06009), the Basque Departamento de Educación, UPV/EHU (Grant No. IT-756-13), Spanish Ministerio de Economia y Competitividad (MINECO Grant No. FIS2016-75862-P), the Saint Petersburg State University grant for scientific investigations (Grant No.15.61.202.2015). M.M.O. acknowledges support by the Diputación Foral de Gipuzkoa (SAREA 2018 - RED 2018*, *Project No. 2018-CIEN-000025-01)

Infrared spectroscopic ellipsometry and optical spectroscopy of plasmons in classic 3D topological insulators

Narrow bandgap BiSe, BiTe, and SbTe, 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 BiSe and SbTe and to fail in the case of a similar compound, BiTe. 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.This work was supported by the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02 and EİF-BGM-3-BRFTF-2+/2017-15/02/1), the Russian Foundation for Basic Research (Grant No. 18-52-06009), and the Saint Petersburg State University grant for scientific investigations (Grant No. 15.61.202.2015)