E. V. Chulkov

Saint Petersburg State University, Sankt-Peterburg, St.-Petersburg, Russia

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Publications (444)1435.88 Total impact

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    ABSTRACT: We present a theoretical study of lifetimes of interface states (IS) on metal-organic interfaces PTCDA/Ag(111), NTCDA/Ag(111), PFP/Ag(111), and PTCDA/Ag(100), describing and explaining the recent experimental data. By means of unfolding the band structure of one of the interfaces under study onto the Ag(111) Brillouin zone we demonstrate, that the Brillouin zone folding upon organic monolayer deposition plays a minor role in the phase space for electron decay, and hence weakly affects the resulting lifetimes. The presence of the unoccupied molecular states below the IS gives a small contribution to the IS decay rate mostly determined by the change of the phase space of bulk states upon the energy shift of the IS. The calculated lifetimes follow the experimentally observed trends. In particular, we explain the trend of the unusual increase of the IS lifetimes with rising temperature.
    Full-text · Article · Dec 2015 · Physical Review B
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    V. N. Men’shov · Victor Tugushev · E.V. Chulkov

    Full-text · Article · Dec 2015 · JETP Letters
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    ABSTRACT: We develop a theory of energy relaxation in semiconductors and insulators highly excited by the long-acting external irradiation. We derive the equation for the non-equilibrium distribution function of excited electrons. The solution for this function breaks up into the sum of two contributions. The low-energy contribution is concentrated in a narrow range near the bottom of the conduction band. It has the typical form of a Fermi distribution with an effective temperature and chemical potential. The effective temperature and chemical potential in this low-energy term are determined by the intensity of carriers' generation, the speed of electron-phonon relaxation, rates of inter-band recombination and electron capture on the defects. In addition, there is a substantial high-energy correction. This high-energy 'tail' covers largely the conduction band. The shape of the high-energy 'tail' strongly depends on the rate of electron-phonon relaxation but does not depend on the rates of recombination and trapping. We apply the theory to the calculation of a non-equilibrium distribution of electrons in irradiated GaN. Probabilities of optical excitations from the valence to conduction band and electron-phonon coupling probabilities in GaN were calculated by the density functional perturbation theory. Our calculation of both parts of distribution function in gallium nitride shows that when the speed of electron-phonon scattering is comparable with the rate of recombination and trapping then the contribution of the non-Fermi 'tail' is comparable with that of the low-energy Fermi-like component. So the high-energy contribution can affect essentially the charge transport in the irradiated and highly doped semiconductors.
    No preview · Article · Dec 2015
  • A. P. Protogenov · E. V. Chulkov
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    ABSTRACT: The N-terminal scheme is considered for studying the contribution of edge states to the response of a two-dimensional topological insulator. A universal distribution of the nonlocal resistance between terminals is determined in the ballistic transport approach. The calculated responses are identical to experimentally observed values. The spectral properties of surface electronic states in Weyl semimetals are also studied. The density of surface states is accurately determined. The universal behavior of these characteristics is a distinctive feature of the considered Dirac materials which can be used in practical applications.
    No preview · Article · Dec 2015 · Semiconductors
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    ABSTRACT: We have investigated plasmonic excitations at the surface of Bi2Se3 (0001) via high-resolution electron energy loss spectroscopy. For low parallel momentum transfer q∥, the loss spectrum shows a distinctive feature peaked at 104 meV. This mode varies weakly with q∥. The behavior of its intensity as a function of primary energy and scattering angle indicates that it is a surface plasmon. At larger momenta (q∥ ∼ 0.04 Å−1), an additional peak, attributed to the Dirac plasmon, becomes clearly defined in the loss spectrum. Momentum-resolved loss spectra provide evidence of the mutual interaction between the surface plasmon and the Dirac plasmon of Bi2Se3. The proposed theoretical model accounting for the coexistence of three-dimensional doping electrons and two-dimensional Dirac fermions accurately represents the experimental observations. The results reveal novel routes for engineering plasmonic devices based on topological insulators.
    Full-text · Article · Nov 2015 · Physical Review Letters
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    ABSTRACT: The modification of the graphene spin structure is of interest for novel possibilities of application of graphene in spintronics. The most exciting of them demand not only high value of spin-orbit splitting of the graphene states, but non-Rashba behavior of the splitting and spatial modulation of the spin-orbit interaction. In this work we study the spin and electronic structure of graphene on Ir(111) with intercalated Pt monolayer. Pt interlayer does not change the 9.3 × 9.3 superlattice of graphene, while the spin structure of the Dirac cone becomes modified. It is shown that the Rashba splitting of the π state is reduced, while hybridization of the graphene and substrate states leads to a spin-dependent avoided-crossing effect near the Fermi level. Such a variation of spin-orbit interaction combined with the superlattice effects can induce a topological phase in graphene.
    Full-text · Article · Oct 2015 · Phys Rev B. Solid State
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    M. M. Otrokov · E. V. Chulkov · A Arnau
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    ABSTRACT: We propose a way to break the time-reversal symmetry at the surface of a three-dimensional topological insulator that combines features of both surface magnetic doping and magnetic proximity effect. Based on the possibility of organizing an ordered array of local magnetic moments by inserting them into a two-dimensional matrix of organic ligands, we study the magnetic coupling and electronic structure of such metal-organic coordination networks on a topological insulator surface from first principles. In this way, we find that both Co and Cr centers, linked by the tetracyanoethylenelike organic ligand, are coupled ferromagnetically and, depending on the distance to the topological insulator substrate, can yield a magnetic proximity effect. This latter leads to the Dirac point gap opening indicative of the time-reversal symmetry breaking.
    Full-text · Article · Oct 2015 · Physical Review B
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    Dataset: SSP.190.494
    V. N. Men’shov · V. V. Tugushev · E. V. Chulkov

    Full-text · Dataset · Sep 2015
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    ABSTRACT: Ab initio study of the adsorption, diffusion, and intercalation of alkali metal adatoms on the (0001) step surface of the topological insulator Bi2Se3 has been performed for the case of low coverage. The calculations of the activation energies of diffusion of adatoms on the surface and in van der Waals gaps near steps, as well as the estimate of diffusion lengths, have shown that efficient intercalation through steps is possible only for Li and Na. Data obtained for K, Rb, and Cs atoms indicate that their thermal desorption at high temperatures can occur before intercalation. The results have been discussed in the context of existing experimental data.
    Full-text · Article · Sep 2015 · Journal of Experimental and Theoretical Physics
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    Full-text · Dataset · Aug 2015
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    ABSTRACT: We report the bulk and surface electronic properties and spin polarization of a rich family of Sn-based ternary topological insulators studied by means of first-principles calculations within the framework of density functional theory. These compounds exist with the following stoichiometries: SnX2Te4,SnX4Te7, and SnBi6Te10 (X = Sb and Bi). Where a septuple layer or a quintuple layer and septuple layer blocks alternate along the hexagonal axis. We reveal that the bulk band gap in these compounds is about 100 meV and recognize a strong dependence of the spin polarization on the cleavage surface. The calculated spin polarization reaches 85% in some cases, that is one of the highest predicted values hitherto. Since the electron spin polarization is a relevant parameter for spintronics technology, this new family is suitable for applications within this field. © 2015 American Physical Society.
    No preview · Article · Jul 2015 · Physical Review B
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    ABSTRACT: The atomic structure of ultrathin iron films deposited on the (0001) surface of the topological insulator Bi2Se3 is analyzed by surface x-ray absorption spectroscopy. Iron atoms deposited on a Bi2Se3 (0001) surface kept at 160 K substitute bismuth atoms within the first quintuple layer. Iron atoms are neighbored by six selenium atoms at a distance in the 2.4 Å range indicating substantial atomic relaxations. Mild annealing up to 520 K leads to the formation of α-FeSe, characterized by a local order extending up to the sixth shell (5.80 Å). Ab initio calculations predict a noncollinear magnetic ordering with a transition temperature of 3.5-10 K depending on the iron concentration and the number of the layers in which Fe is located.
    Full-text · Article · Jul 2015 · Physical review. B, Condensed matter
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    ABSTRACT: An exotic type of topological spin-helical surface state was found in layered van der Waals bonded (SnTe)n=2,3(Bi2Te3)m=1 compounds which comprise two covalently bonded band inverted sublattices, SnTe and Bi2Te3, within a building block. This topological state demonstrates unusual dispersion within the band gap. The dispersion of the surface state has two linear sections of different slope with a shoulder feature between them. Such a dispersion of the topological surface state enables an effective switch of the velocity of topological carriers by means of applying an external electric field.
    No preview · Article · Jun 2015 · Physical Review B
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    S.V. Eremeev · V.N. Men׳shov · V.V. Tugushev · E.V. Chulkov
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    ABSTRACT: By means of relativistic density functional theory (DFT) calculations we study electron band structure of the topological insulator (TI) Bi2Se3 thin films deposited on the ferromagnetic insulator (FMI) EuS substrate. In the Bi2Se3/EuS heterostructure, the gap opened in the spectrum of the topological state has a hybridization character and is shown to be controlled by the Bi2Se3 film thickness, while magnetic contribution to the gap is negligibly small. We also analyzed the effect of Eu doping on the magnetization of the Bi2Se3 film and demonstrated that the Eu impurity induces magnetic moments on neighboring Se and Bi atoms an order of magnitude larger than the substrate-induced moments. Recent magnetic and magneto-transport measurements in EuS/Bi2Se3 heterostructure are discussed.
    Full-text · Article · Jun 2015 · Journal of Magnetism and Magnetic Materials
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    ABSTRACT: We report first-principles GW results on the dispersion of the bulk band-gap edges in the three-dimensional topological insulator Sb2Te3. We find that, independently of the reference density-functional-theory band structure and the crystal-lattice parameters used, the one-shot GW corrections enlarge the fundamental band gap, bringing its value in close agreement with experiment. We conclude that the GW corrections cause the displacement of the valence-band maximum (VBM) to the Γ point, ensuring that the surface-state Dirac point lies above the VBM. We extend our study to the analysis of the electron-energy-loss spectrum (EELS) of bulk Sb2Te3. In particular, we perform energy-filtered transmission electron microscopy and reflection EELS measurements. We show that the random-phase approximation with the GW quasiparticle energies and taking into account virtual excitations from the semicore states leads to good agreement with our experimental data.
    Full-text · Article · Jun 2015 · Physical Review B
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    ABSTRACT: A new type of topological spin-helical surface states was discovered in layered van der Waals bonded (SnTe)$_{n=2,3}$(Bi$_2$Te$_3$)$_{m=1}$ compounds which comprise two covalently bonded band inverted subsystems, SnTe and Bi$_2$Te$_3$, within a building block. This novel topological states demonstrate non-Dirac dispersion within the band gap. The dispersion of the surface state has two linear sections of different slope with shoulder feature between them. Such a dispersion of the topological surface state enables effective switch of the velocity of topological carriers by means of applying an external electric field.
    Full-text · Article · May 2015
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    ABSTRACT: A bilayer of bismuth is recognized as a prototype two-dimensional topological insulator. Here we present a simple and well reproducible top-down approach to prepare a flat and well ordered bismuth bilayer with a lateral size of several hundred nanometers on ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$(0001). Using scanning tunneling microscopy, surface x-ray diffraction, and Auger electron spectroscopy we show that exposure of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$(0001) to atomic hydrogen completely removes selenium from the top quintuple layer. The band structure of the system, calculated from first principles for the experimentally derived atomic structure, is in excellent agreement with recent photoemission data. Our results open interesting perspectives for the study of topological insulators in general.
    No preview · Article · May 2015 · Physical Review B
  • G.G. Rusina · S.D. Borisova · E.V. Chulkov
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    ABSTRACT: The binding energy, equilibrium geometry, and vibration frequencies in bimetallic clusters Ni13 − nAln (n = 0–13) have been calculated using the embedded atom method potentials. It has been shown that the icosahedral structure is the most stable in monoatomic and bimetallic clusters. A tendency of Al atoms to segregate on the cluster surface has been revealed in agreement with the experimental data. The calculations of the atomic vibrations have shown the nonmonotonic dependence of the minimum and maximum vibration frequencies of cluster atoms on its composition and the coupling of their extreme values with the most stable atomic configuration. The increase in the number of Al atoms leads to the shift of the frequency spectrum and the substantial redistribution of the localization of vibrations on the cluster atoms.
    No preview · Article · Apr 2015 · JETP Letters
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    ABSTRACT: The dielectric and optical properties of semiconductor compounds BiTeI and BiTeCl have been studied the� oretically within time dependent density functionaltheory and experimentally by spectral ellipsometry. Anisotropy of dielectric constants in the long�wavelength limit and dispersion of the σand σ+ πbulk plas� mons in the longitudinal and transverse directions of the crystals have been discovered. It has been shown that the inclusion of the spin–orbit interaction is necessary for agreement between the theory and the results of optical measurements.
    Full-text · Article · Apr 2015 · JETP Letters
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    ABSTRACT: Modifications in dielectric properties of palladium upon absorption of hydrogen are investigated theoretically in the low-energy (0-2 eV) region. The calculations were performed with full inclusion of the electronic band structure obtained within a self-consistent pseudopotential approach. In particular, we trace the evolution of the acoustic-like plasmon (AP) found previously in clean Pd with increasing hydrogen concentration. It exists in PdHx up to the hydrogen content x corresponding to the complete filling of the 4d Pd-derived energy bands because of the presence of two kinds of carriers at the Fermi surface. At higher H concentration the AP disappears since only one kind of carrier within the sp-like energy band exists at the Fermi level. Additionally, we investigate the spatial distribution inside the crystal of a potential caused by a time-dependent external perturbation and observe drastic modifications in the screening properties in the PdHx systems with energy and with hydrogen concentration.
    Full-text · Article · Feb 2015 · Journal of Physics Condensed Matter

Publication Stats

9k Citations
1,435.88 Total Impact Points

Institutions

  • 2015
    • Saint Petersburg State University
      Sankt-Peterburg, St.-Petersburg, Russia
    • Tomsk Polytechnical University
      Tomsk, Tomsk, Russia
  • 1994-2015
    • Universidad del País Vasco / Euskal Herriko Unibertsitatea
      • • Departamento de Física de Materiales
      • • Facultad de Química
      Leioa, Basque Country, Spain
  • 1979-2015
    • Tomsk State University
      Tomsk, Tomsk, Russia
  • 2001-2014
    • Donostia International Physics Center
      San Sebastián, Basque Country, Spain
  • 2011
    • Novosibirsk State University
      • Department of Physics
      Novo-Nikolaevsk, Novosibirsk, Russia
  • 2010
    • Università degli Studi di Milano-Bicocca
      • Department of Materials Science
      Milano, Lombardy, Italy
    • Ikerbasque - Basque Foundation for Science
      Bilbo, Basque Country, Spain
  • 2007-2010
    • Center of Materials Physics
      San Sebastián, Basque Country, Spain
  • 2009
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
  • 2002
    • Philipps University of Marburg
      • Faculty of Physics
      Marburg, Hesse, Germany
  • 1987-1998
    • Russian Academy of Sciences
      • Institute of Strength Physics and Materials Science of the Siberian Branch
      Moscow, Moscow, Russia