E. V. Chulkov

Universidad del País Vasco / Euskal Herriko Unibertsitatea, Leioa, Basque Country, Spain

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Publications (421)1414.1 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.
  • Physical review. B, Condensed matter 07/2015; 92:045423. DOI:10.1103/PhysRevB.92.045423 · 3.66 Impact Factor
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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.
    Physical review. B, Condensed matter 06/2015; 91:245123. DOI:10.1103/PhysRevB.91.245123 · 3.66 Impact Factor
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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.
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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.
    Physical Review B 05/2015; 91(20):205430. DOI:10.1103/PhysRevB.91.205430 · 3.74 Impact Factor
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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.
    Journal of Physics Condensed Matter 02/2015; 27(5):055501. DOI:10.1088/0953-8984/27/5/055501 · 2.35 Impact Factor
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    ABSTRACT: In the frame of k .p method and variational approach for the effective energy functional of a contact between a three-dimensional topological insulator (TI) and normal insulator (NI), we analytically describe the formation of interfacial bound electron states of two types (ordinary and topological) having different spatial distributions and energy spectra. We show that these states appear as a result of the interplay of two factors: hybridization and band bending of the TI and NI electron states near the TI/NI boundary. These results are corroborated by the density functional theory calculations for the exemplar Bi2Se3/Zn Se system.
    Physical Review B 02/2015; 91(7). DOI:10.1103/PhysRevB.91.075307 · 3.74 Impact Factor
  • V G Tyuterev · V P Zhukov · P M Echenique · E V Chulkov
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    ABSTRACT: The electron energy relaxation in semiconductors and insulators after high-level external excitation is analysed by a semi-classical approach based on a kinetic equation of the Boltzmann type. We show that the non-equilibrium distributions of electrons and holes have a customary Fermi-like shape with some effective temperature but also possess a high-energy non-Fermian 'tail'. The latter may extend deep into the conduction and valence bands while the Fermi-like component is localized within a small energy range just above the edge of the band gap. The effective temperature, effective chemical potential, and the shape of the high-energy component are governed by the process of electron-phonon interactions as well as by the rates of carrier generation and inter-band radiative recombination.
    Journal of Physics Condensed Matter 01/2015; 27(2):025801. DOI:10.1088/0953-8984/27/2/025801 · 2.35 Impact Factor
  • J. Reimann · J. Güdde · K. Kuroda · E. V. Chulkov · U. Höfer
    Physical Review B 01/2015; 91(3). DOI:10.1103/PhysRevB.91.039903 · 3.74 Impact Factor
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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.
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    ABSTRACT: The electronic and spin structure of a graphene monolayer synthesized on Pt(111) has been investigated experimentally by angle-and spin-resolved photoemission with different polarizations of incident synchrotron radiation and using density functional theory calculations. It is shown that despite the observed total quasifreestanding character of the dispersion of the graphene π state remarkable local distortions and breaks in the dispersions take place due to hybridization between the graphene π and Pt d states. Corresponding spin-dependent avoided-crossing effects lead to significant modification of the spin structure and cause an enhanced induced spin-orbit splitting of the graphene π states near the Fermi level in the region of the ¯ K point of the graphene Brillouin zone (BZ) with a magnitude of 80–200 meV depending on the direction in the BZ. Using p, s, and elliptical polarizations of the synchrotron radiation, the contributions of the graphene π and Pt d states were separated and their intersection at the Fermi level, which is important for effective spin injection between these states, was shown. Moreover, analysis of the data allows us to conclude that in the region of the Dirac point the spin structure of the system cannot be described by a Rashba splitting, and even a spin-orbit gap between lower and upper Dirac cones is observed.
    Physical Review B 12/2014; 22(75). DOI:10.1103/PhysRevB.90.235431 · 3.74 Impact Factor
  • D P Borisov · A D Korotaev · V M Kuznetsov · E V Chulkov
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    ABSTRACT: The design of an electrode system and the characteristics of a gas-discharge plasma source (generator) based on an arc discharge in gas sustained by thermionic emission are presented. The results of an experimental investigation of the service life of a thermionic (hot) cathode of the plasma generator are reported as a function of the discharge current and voltage and the cathode filament power. It is shown that an increase in the burning voltage from 28 to 60 V considerably reduces the service life of the hot cathode, while the discharge current and the cathode filament power exert a less critical effect on its lifetime. The conditions necessary for achieving long-term service life parameters and high efficiency of plasma generation are found out.
    Journal of Physics Conference Series 11/2014; 552(1):012001. DOI:10.1088/1742-6596/552/1/012001
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    ABSTRACT: We present a surface x-ray analysis of the atomic structure of the (0001) surface of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, which was grown as a single crystal and as an ultrathin film on Si(111) using molecular beam epitaxy (MBE). In general we find that the top Se-Bi layer spacing is expanded between 2% and 17% relative to the bulk, while deeper layers and the first van der Waals gap are unrelaxed. The top layer expansion is directly related to the amount of surface contamination by carbon and oxygen. The near-surface structures of the single crystal and the MBE-grown thin film differ in the degree of (static) disorder: for the former an overall Debye parameter ($B$) per quintuple layer (QL) of $5\phantom{\rule{0.28em}{0ex}}{\AA{}}^{2}$ is found to decrease slowly with depth. MBE-grown ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ films exhibit the opposite scenario, characterized by an increase in $B$ from about $10\phantom{\rule{0.28em}{0ex}}{\AA{}}^{2}$ for the topmost QL to values of $B=20\char21{}40 {\AA{}}^{2}$ for the fourth QL. This is attributed to the lattice misfit to the Si(111) surface. Ab initio calculations reveal carbon to act as an $n$-dopant, while the first interlayer spacing expansion induces a shift of the Dirac point towards the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ bulk conduction band minimum.
    Physical Review B 10/2014; 90(15):155456. DOI:10.1103/PhysRevB.90.155456 · 3.74 Impact Factor
  • G. G. Rusina · S. D. Borisova · E. V. Chulkov
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    ABSTRACT: The atomic and phonon structures of a Pb ultrathin film on the Al(100) surface have been theoretically studied. Surface relaxation, local density of vibrational states, and polarization of the phonon modes of adatoms and atoms of a substrate have been discussed. It has been shown that the adsorption of Pb results in the oscillating relaxation of the surface of the substrate and warping of the structure in subsurface layers. Comparative analysis of the vibrational characteristics of the pure surface of the substrate and the surface with adatoms has shown that the adsorptive interaction in the system and its dynamic stability are governed by new vibrational modes that are not inherent in pure Al and Pb surfaces.
    JETP Letters 10/2014; 100(4):237-241. DOI:10.1134/S0021364014160139 · 1.36 Impact Factor
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    ABSTRACT: Collective vibrational modes of crystal lattices, called phonons, determine fundamental material properties, such as their thermal and electrical conductivities. Bulk phonon spectra are influenced by point defects. More recently, the importance of phonons on nanostructures has come into the focus of attention. Here we show a spatially resolved phonon spectra of point defects that reveal distinctly different signatures for a cavity alone and an impurity atom fully integrated into the surface as opposed to one placed into a cavity. The spectra are indicative for delocalized phonons and localized vibrations, respectively, as confirmed by theory.
    Nature Communications 10/2014; 5:5089. DOI:10.1038/ncomms6089 · 10.74 Impact Factor
  • X. Zubizarreta · V. M. Silkin · E. V. Chulkov
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    ABSTRACT: An ab initio study of the dynamical dielectric response of bulk lead is presented. The influence of the $5d$ semicore states on the characteristics of the bulk plasmon is analyzed by means of first-principles pseudopotential calculations. The effects of spin-orbit interactions and local-fields are also studied in detail. The inclusion of the $5d$ semicore states in the valence configuration completely changes the high-energy-transfer dielectric properties of bulk Pb. In particular, it lowers the computed bulk plasmon energy by about 3.5 eV, bringing its frequency to good agreement with experimental data. In general, the high-energy-transfer dielectric response of bulk Pb is found to be shaped mostly by the interplay between the interband transitions involving the semicore $5d$ states and the spin-orbit coupling interaction. Local-field effects are found to affect the relative spectral weight of the high-energy excitations, while leaving their dispersion mostly unaffected.
    Physical Review B 10/2014; 90(16). DOI:10.1103/PhysRevB.90.165121 · 3.74 Impact Factor
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    ABSTRACT: We present a comprehensive ab initio study of structural, electronic, lattice dynamical and electron-phonon coupling properties of the Bi(111) surface within density functional perturbation theory. Relativistic corrections due to spin-orbit coupling are consistently taken into account. As calculations are carried out in a periodic slab geometry, special attention is given to the convergence with respect to the slab thickness. Although the electronic structure of Bi(111) thin films varies significantly with thickness, we found that the lattice dynamics of Bi(111) is quite robust and appears converged already for slabs as thin as 6 bilayers. Changes of interatomic couplings are confined mostly to the first two bilayers, resulting in super-bulk modes with frequencies higher than the optic bulk spectrum, and in an enhanced density of states at lower frequencies for atoms in the first bilayer. Electronic states of the surface band related to the outer part of the hole Fermi surfaces exhibit a moderate electron-phonon coupling of about 0.45, which is larger than the coupling constant of bulk Bi. States at the inner part of the hole surface as well as those forming the electron pocket close to the zone center show much increased couplings due to transitions into bulk projected states near Gamma_bar. For these cases, the state dependent Eliashberg functions exhibit pronounced peaks at low energy and strongly deviate in shape from a Debye-like spectrum, indicating that an extraction of the coupling strength from measured electronic self-energies based on this simple model is likely to fail.
    Physical Review B 09/2014; 90(19). DOI:10.1103/PhysRevB.90.195438 · 3.74 Impact Factor
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    ABSTRACT: Angular resolved photoemission spectroscopy in combination with ab initio calculations show that trace amounts of carbon doping of the Bi_{2}Se_{3} surface allows the controlled shift of the Dirac point within the bulk band gap. In contrast to expectation, no Rashba-split two-dimensional electron gas states appear. This unique electronic modification is related to surface structural modification characterized by an expansion of the top Se-Bi spacing of ≈11% as evidenced by surface x-ray diffraction. Our results provide new ways to tune the surface band structure of topological insulators.
    Physical Review Letters 09/2014; 113:116802. · 7.51 Impact Factor
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    ABSTRACT: Angular resolved photoemission spectroscopy in combination with ab initio calculations show that trace amounts of carbon doping of the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ surface allows the controlled shift of the Dirac point within the bulk band gap. In contrast to expectation, no Rashba-split two-dimensional electron gas states appear. This unique electronic modification is related to surface structural modification characterized by an expansion of the top Se-Bi spacing of $\ensuremath{\approx}11%$ as evidenced by surface x-ray diffraction. Our results provide new ways to tune the surface band structure of topological insulators.
    Physical Review Letters 09/2014; 113(11). DOI:10.1103/PhysRevLett.113.116802 · 7.51 Impact Factor

Publication Stats

7k Citations
1,414.10 Total Impact Points

Institutions

  • 1997–2015
    • Universidad del País Vasco / Euskal Herriko Unibertsitatea
      • Departamento de Física de Materiales
      Leioa, Basque Country, Spain
  • 1979–2015
    • Tomsk State University
      Tomsk, Tomsk, Russia
  • 2001–2014
    • Donostia International Physics Center
      San Sebastián, Basque Country, Spain
  • 2011
    • University of Antioquia
      Santa Fe de Antioquia, Antioquia, Colombia
  • 2010
    • Università degli Studi di Milano-Bicocca
      • Department of Materials Science
      Milano, Lombardy, Italy
    • Ikerbasque - Basque Foundation for Science
      Bilbo, Basque Country, Spain
  • 2008–2010
    • Center of Materials Physics
      San Sebastián, Basque Country, Spain
  • 2009
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
  • 1987–1998
    • Russian Academy of Sciences
      • Institute of Strength Physics and Materials Science of the Siberian Branch
      Moscow, Moscow, Russia