The quasiparticle band gap in the topological insulator Bi2Te3

We present a theoretical study of dispersion of states which form the bulk band-gap edges in the three-dimensional topological insulator Bi2Te3. Within density functional theory, we analyze the effect of atomic positions varying within the error range of the available experimental data and approximation chosen for the exchange-correlation functional on the bulk band gap and k-space location of valence- and conduction-band extrema. For each set of the positions with different exchange-correlation functionals, we show how many-body corrections calculated within a one-shot GW approach affect the mentioned characteristics of electronic structure of Bi2Te3. We thus also illustrate to what degree the one-shot GW results are sensitive to the reference one-particle band structure in the case of bismuth telluride. We found that for this topological insulator the GW corrections enlarge the fundamental band gap and for certain atomic positions and reference band structure bring its value in close agreement with experiment.Comment: 12 pages, 6 figures, 5 table

Competing rhombohedral and monoclinic crystal structures in MnPn2Ch4Pn_2Ch_4 compounds: an {\em ab-initio} study

Based on the relativistic spin-polarized density functional theory calculations we investigate the crystal structure, electronic and magnetic properties of a family MnPn2Ch4 compounds, where pnictogen metal atoms (Pn) are Sb and Bi; chalcogens (Ch) are Se, Te. We show that in the series the compounds of this family with heavier elements prefer to adopt rhombohedral crystal structure composed of weakly bonded septuple monoatomic layers while those with lighter elements tend to be in the monoclinic structure. Irrespective of the crystal structure all compounds of the MnPn2Ch4 series demonstrate a weak energy gain (of a few meV per formula unit or even smaller than meV) for antiferromagnetic (AFM) coupling for magnetic moments on Mn atoms with respect to their ferromagnetic (FM) state. For rhombohedral structures the interlayer AFM coupling is preferable while in monoclinic phases intralayer AFM configuration with ferromagnetic ordering along the Mn chain and antiferromagnetic ordering between the chains has a minimum energy. Over the series the monoclinic compounds are characterized by substantially wider bandgap than compounds with rhombohedral structure

Electron-phonon interaction at the Be(0001) surface

We present a first principle study of the electron-phonon (e-p) interaction at the Be(0001) surface. The real and imaginary part of the e-p self energy are calculated for the surface state in the binding energy range from the $\bar{\Gamma}$ point to the Fermi level. Our calculation shows an overall good agreement with several photoemission data measured at high and low temperatures. Additionally, we show that the energy derivative of real part of the self-energy presents a strong temperature and energy variation close to $E_{F}$, making it difficult to measure its value just at $E_{F}$.Comment: Accepted in Phys. Rev. Lett., 5 figure

Spin-helical Dirac states in graphene induced by polar-substrate surfaces with giant spin-orbit interaction: a new platform for spintronics

Spintronics, or spin electronics, is aimed at efficient control and manipulation of spin degrees of freedom in electron systems. To comply with demands of nowaday spintronics, the studies of electron systems hosting giant spin-orbit-split electron states have become one of the most important directions providing us with a basis for desirable spintronics devices. In construction of such devices, it is also tempting to involve graphene, which has attracted great attention because of its unique and remarkable electronic properties and was recognized as a viable replacement for silicon in electronics. In this case, a challenging goal is to make graphene Dirac states spin-polarized. Here, we report on absolutely new promising pathway to create spin-polarized Dirac states based on coupling of graphene and polar-substrate surface states with giant Rashba-type spin-splitting. We demonstrate how the spin-helical Dirac states are formed in graphene deposited on the surface of BiTeCl. This coupling induces spin separation of the originally spin-degenerate graphene states and results in fully helical in-plane spin polarization of the Dirac electrons.Comment: 5 pages, 3 figure

Rashba split surface states in BiTeBr

Within density functional theory, we study bulk band structure and surface states of BiTeBr. We consider both ordered and disordered phases which differ in atomic order in the Te-Br sublattice. On the basis of relativistic ab-initio calculations, we show that the ordered BiTeBr is energetically preferable as compared with the disordered one. We demonstrate that both Te- and Br-terminated surfaces of the ordered BiTeBr hold surface states with a giant spin-orbit splitting. The Te-terminated surface-state spin splitting has the Rashba-type behavior with the coupling parameter \alpha_R ~ 2 eV\AA.Comment: 8 pages, 7 figure