Publications (414)1393.62 Total impact
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ABSTRACT: We report firstprinciples GW results on the dispersion of the bulk bandgap edges in the threedimensional topological insulator Sb2Te3. We find that, independently of the reference densityfunctionaltheory band structure and the crystallattice parameters used, the oneshot 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 valenceband maximum (VBM) to the Γ point, ensuring that the surfacestate Dirac point lies above the VBM. We extend our study to the analysis of the electronenergyloss spectrum (EELS) of bulk Sb2Te3. In particular, we perform energyfiltered transmission electron microscopy and reflection EELS measurements. We show that the randomphase 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  [Show abstract] [Hide abstract]
ABSTRACT: A new type of topological spinhelical 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 nonDirac 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.  [Show abstract] [Hide abstract]
ABSTRACT: A bilayer of bismuth is recognized as a prototype twodimensional topological insulator. Here we present a simple and well reproducible topdown 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 xray 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 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Modifications in dielectric properties of palladium upon absorption of hydrogen are investigated theoretically in the lowenergy (02 eV) region. The calculations were performed with full inclusion of the electronic band structure obtained within a selfconsistent pseudopotential approach. In particular, we trace the evolution of the acousticlike 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 Pdderived 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 splike energy band exists at the Fermi level. Additionally, we investigate the spatial distribution inside the crystal of a potential caused by a timedependent 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:10.1088/09538984/27/5/055501 · 2.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In the frame of k .p method and variational approach for the effective energy functional of a contact between a threedimensional 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 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The electron energy relaxation in semiconductors and insulators after highlevel external excitation is analysed by a semiclassical approach based on a kinetic equation of the Boltzmann type. We show that the nonequilibrium distributions of electrons and holes have a customary Fermilike shape with some effective temperature but also possess a highenergy nonFermian 'tail'. The latter may extend deep into the conduction and valence bands while the Fermilike 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 highenergy component are governed by the process of electronphonon interactions as well as by the rates of carrier generation and interband radiative recombination.Journal of Physics Condensed Matter 01/2015; 27(2):025801. DOI:10.1088/09538984/27/2/025801 · 2.22 Impact Factor  Physical Review B 01/2015; 91(3). DOI:10.1103/PhysRevB.91.039903 · 3.66 Impact Factor
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ABSTRACT: The electronic and spin structure of a graphene monolayer synthesized on Pt(111) has been investigated experimentally by angleand spinresolved 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 spindependent avoidedcrossing effects lead to significant modification of the spin structure and cause an enhanced induced spinorbit 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 spinorbit gap between lower and upper Dirac cones is observed.Physical Review B 12/2014; 22(75). DOI:10.1103/PhysRevB.90.235431 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The design of an electrode system and the characteristics of a gasdischarge 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 longterm service life parameters and high efficiency of plasma generation are found out.Journal of Physics Conference Series 11/2014; 552(1):012001. DOI:10.1088/17426596/552/1/012001  Physical Review B 10/2014; 90:155456. DOI:10.1103/PhysRevB.90.155456 · 3.66 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 
Article: Effects of 5 d electrons and spinorbit interaction on the characteristics of bulk plasmons in lead
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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 firstprinciples pseudopotential calculations. The effects of spinorbit interactions and localfields are also studied in detail. The inclusion of the $5d$ semicore states in the valence configuration completely changes the highenergytransfer 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 highenergytransfer 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 spinorbit coupling interaction. Localfield effects are found to affect the relative spectral weight of the highenergy excitations, while leaving their dispersion mostly unaffected.Physical Review B 10/2014; 90(16). DOI:10.1103/PhysRevB.90.165121 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a comprehensive ab initio study of structural, electronic, lattice dynamical and electronphonon coupling properties of the Bi(111) surface within density functional perturbation theory. Relativistic corrections due to spinorbit 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 superbulk 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 electronphonon 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 Debyelike spectrum, indicating that an extraction of the coupling strength from measured electronic selfenergies based on this simple model is likely to fail.Physical Review B 09/2014; 90(19). DOI:10.1103/PhysRevB.90.195438 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
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 Rashbasplit twodimensional electron gas states appear. This unique electronic modification is related to surface structural modification characterized by an expansion of the top SeBi spacing of ≈11% as evidenced by surface xray diffraction. Our results provide new ways to tune the surface band structure of topological insulators.Physical Review Letters 09/2014; 113:116802. · 7.73 Impact Factor 
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ABSTRACT: The electron–phonon coupling parameters in the vicinity of the point, , for electronic quantum well states in epitaxial lead films on a Si(1 1 1) substrate are measured using 5, 7 and 12 ML films and femtosecond laser photoemission spectroscopy. The values in the range of 0.6–0.9 were obtained by temperaturedependent line width analysis of occupied quantum well states and found to be considerably smaller than the momentum averaged electron–phonon coupling at the Fermi level of bulk lead, (λ = 1.1–1.7). The results are compared to density functional theory calculations of the lead films with and without interfacial stress. It is shown that the discrepancy can not be explained by means of confinement effects or simple structural modifications of the Pb films and, thus, is attributed to the influence of the substrate on the Pb electronic and vibrational structures.Journal of Physics Condensed Matter 08/2014; 26(35):352001. DOI:10.1088/09538984/26/35/352001 · 2.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The topological insulators Bi2Se3 and Bi2Te2Se have been shown to possess unoccupied topological surface states at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Using timeresolved twophoton photoemission we study the electron dynamics of the unoccupied topological surface states, imagepotential states and conduction bands on these surfaces.Journal of Electron Spectroscopy and Related Phenomena 08/2014; 195. DOI:10.1016/j.elspec.2014.03.013 · 1.55 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The unoccupied electronic structure of epitaxial Pb films on Si(111) is analyzed by angleresolved twophoton photoemission in the Γ¯ → M¯ direction close to the Brillouin zone center. The experimental results are compared to density functional theory calculations and we focus on the nature of the interaction of the 6p z states with the Si substrate. The experimentally obtained dispersion E (k ) of the unoccupied quantum well states is weaker than expected for freestanding films, in good agreement with their occupied counterparts. Following E (k ) of quantum well states as a function of momentum at different energies, which are degenerate and nondegenerate with the Si conduction band, we observe no influence of the Si bulk band and conclude a vanishing direct interaction of the Pb 6p z states with the Si band. However, the momentum range at which mixing of 6p z and 6p x,y derived subbands is found to occur in the presence of the Si substrate is closer to Γ¯ than in the corresponding freestanding film, which indicates a substratemediated enhancement of the mixing of these states. Additional femtosecond timeresolved measurements show a constant relaxation time of hot electrons in unoccupied quantum well states as a function of parallel electron momentum which supports our conclusion of a px,y mediated interaction of the pz states with the Si conduction band.Journal of Electron Spectroscopy and Related Phenomena 08/2014; 195. DOI:10.1016/j.elspec.2014.04.006 · 1.55 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Time and angleresolved twophoton photoemission (2PPE) was used to study the electronic structure and ultrafast electron dynamics of the $p$doped topological insulator ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ and its derivative ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{2}\mathrm{S}$. Our 2PPE experiments directly reveal that the massless Diraccone like energy dispersion of topological surface states is realized above the Fermi energy in both materials. The observed bulk conduction bands of ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{2}\mathrm{S}$ are found to be shifted to higher energies as compared to ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$. This shift has, however, surprisingly almost no influence on the electron dynamics in the topological surface state, which proceed on a picosecond time scale.Physical Review B 08/2014; 90(8). DOI:10.1103/PhysRevB.90.081106 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: By means of relativistic density functional theory (DFT) calculations we study electron band structure of the topological insulator (TI) Bi$_2$Se$_3$ thin films deposited on the ferromagnetic insulator (FMI) EuS substrate. In the Bi$_2$Se$_3$/EuS heterostructure, the gap opened in the spectrum of the topological state has a hybridization character and is shown to be controlled by the Bi$_2$Se$_3$ film thickness, while magnetic contribution to the gap is negligibly small. We also analyzed the effect of Eu doping on the magnetization of the Bi$_2$Se$_3$ film and demonstrated that the Eu impurity induces magnetic moments on neighboring Se and Bi atoms an order of magnitude larger than the substrateinduced moments. Recent magnetic and magnetotransport measurements in EuS/Bi$_2$Se$_3$ heterostructure are discussed.
Publication Stats
7k  Citations  
1,393.62  Total Impact Points  
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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 MilanoBicocca
 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
