Features of the Electronic Structure of the Bi2Se3 Topological Insulator Digitally Doped with 3d Transition Metals

The electronic and optical spectra of the Bi3Se2 topological insulator digitally doped with V, Cr, Mn, Fe, and Co atoms are calculated using density functional theory. It is shown that the introduction of magnetic atoms into separate delta layers (one per 2–9 Bi2Se3 quintuple layers) multiply enhances magnetic effects. A special emphasis is put on Mn doping, which gives rise to the ferromagnetic spin ordering. The sensitivity of the spin order to the concentration and location of magnetic atoms is revealed. The study of an analytical model describing the resonant scattering of electrons in Bi2Se3 by atomic layers of transition metals also suggests the existence of spin-polarized states within the Bi2Se3 band gap. Our ab initio calculations show that transitions between the nested branches of the electronic spectrum, which exist near the Fermi level, are responsible for features of the optical conductivity at -ω ≈ 0.15−0.3eV, the infrared plasmon, and the Kerr angle θK > 12° in the infrared spectral range.