L. Despont

Jožef Stefan Institute, Lubliano, Ljubljana, Slovenia

Are you L. Despont?

Claim your profile

Publications (18)55.84 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a new high-resolution angle-resolved photoemission study of 1T-TiSe2 in both its room-temperature, normal phase and its low-temperature, charge-density wave phase. At low temperature the photoemission spectra are strongly modified, with large band renormalizations at high-symmetry points of the Brillouin zone and a very large transfer of spectral weight to backfolded bands. A calculation of the theoretical spectral function for an excitonic insulator phase reproduces the experimental features with very good agreement. This gives strong evidence in favor of the excitonic insulator scenario as a driving force for the charge-density wave transition in 1T-TiSe2.
    Physical Review Letters 11/2007; 99(14):146403. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A review is given of recent angle-resolved photoemission (ARPES) experiments and analyses on a series of layered charge density wave materials. Important aspects of ARPES are recalled in view of its capability for bulk band, Fermi surface and spectral function mapping despite its surface sensitivity. Discussed are TaS2, TaSe2, NbTe2, TiSe2 and TiTe2 with structures related to the so-called 1T polytype. Many of them undergo charge density wave transitions or exist with a distorted lattice structure. Attempts to explain the mechanism behind the structural reconstruction are given. Depending on the filling of the lowest occupied band a drastically different behaviour is observed. Whereas density functional calculations of the electronic energy and momentum distribution reproduce well the experimental spectral weight distribution at the Fermi energy, the ARPES energy distribution curves reveal that for some of the compounds the Fermi surface is pseudo-gapped. Two different explanations are given, the first based on density functional calculations accounting for the charge-density-wave-induced lattice distortion and the second relying on many-body physics and polaron formation. Qualitatively, both describe the observations well. However, in the future, in order to be selective, quantitative modelling will be necessary, including the photoemission matrix elements.
    Journal of Physics Condensed Matter 08/2007; 19(35):355002. · 2.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Self-assembled arrays of atomic chains on Si(111) represent a fascinating family of nanostructures with quasi-one-dimensional electronic properties. These surface reconstructions are stabilized by a variety of adsorbates ranging from alkali and alkaline earth metals to noble and rare earth metals. Combining the complementary strength of dynamical low-energy electron diffraction, scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we recently showed that besides monovalent and divalent adsorbates, trivalent adsorbates are also able to stabilize silicon honeycomb chains. Consequently silicon honeycomb chains emerge as a most stable, universal building block shared by many atomic chain structures. We here present the systematics behind the self-assembly mechanism of these chain systems and relate the valence state of the adsorbate to the accessible symmetries of the chains.
    Journal of Physics Conference Series 07/2007;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The authors investigated a 1 μm thick molecular beam epitaxy–grown InN film by means of full hemispherical x-ray photoelectron diffraction and high resolution x-ray diffraction. While x-ray diffraction reveals that this nominally hexagonal InN layer contains roughly 1% of cubic phase InN, a comparison between measured and simulated x-ray photoelectron diffraction data allowed them to directly determine the polarity of the crystal. Furthermore, the data indicate that the InN surface consists of a mosaic of domains oriented at an azimuth of 180° to each other, where the azimuth corresponds to the rotation angle around the [0001] axis.
    Applied Physics Letters 05/2007; 90(19):191912-191912-3. · 3.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Fermi surface topology of the layered superconducting charge density wave compound ZrTe3is investigated by angle resolved photoelectron spectroscopy and density functional theory. The Fermi surface is dominated by bands originating from two perpendicular systems of quasi one-dimensional chains. Nesting and opening of a pseudogap at temperatures as high as 250 K are signatures of a Peierls transition in one of these chains. The nesting properties are also studied for high pressure simulated crystal structure.
    Journal of Alloys and Compounds 01/2007; 442(1):268-271. · 2.73 Impact Factor
  • Source
    Applied Physics Letters 01/2007; 90:052907. · 3.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Finite size effects in ferroelectric thin films have been probed in a series of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down to 28 A˚ (seven unit cells). The evolution of the film tetragonality c/a, studied using high resolution x-ray diffraction measurements, shows first a decrease of c/a with decreasing film thickness followed by a recovery of c/a at small thicknesses. This recovery is accompanied by a change from a monodomain to a polydomain configuration of the polarization, as directly demonstrated by piezoresponse atomic force microscopy measurements.
    Applied Physics Letters 01/2007; 90. · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The temperature dependence of the electronic structure of the quasi-two-dimensional material 1T-TaS2 is revisited by considering angle-resolved photoemission spectroscopy (ARPES) and density functional theory to calculate the imaginary part of the static electronic susceptibility characterizing the nesting strength. While nesting appears to play a role in the high temperature phase, the ARPES line shapes reveal peculiar spectral properties which are not consistent with the standard two-dimensional Peierls scenario for the formation of a charge density wave. The temperature dependence of these anomalous spectral features suggests a lattice-distortion enhanced electron-phonon interaction.
    Physical review. B, Condensed matter 10/2006; · 3.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Multiple scattering theory based on a cluster model is used to simulate full hemispherical X-ray photoelectron diffraction measurements on a 1T-TaS 2 (0001) surface. Key points to determine the surface termination are discussed. As the commonly applied single scattering simulations do not give satisfying results, a multiple scattering approach has to be used to accurately simulate the full hemispherical photoelectron diffraction patterns. Differences and similarities between calculations of Ta and S terminated surfaces are presented along with experimental results at room temperature using both, the single and the multiple scattering approaches. We find that the surface is S terminated and that the quantitative difference between the calculations for both terminations permits to show the limits of the single scattering approach for solving surface termination problems. Moreover, by generalizing the results obtained using the multiple scattering approach, we discuss the application of this method to other similar systems. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006
    Physics of Condensed Matter 08/2006; 52(3):421-426. · 1.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Multiple scattering theory based on a cluster model is used to simulate full-hemispherical X-ray photoelectron diffraction measurements in order to verify how state of the art multiple scattering simulations are able to reproduce the experiment. This approach is applied to the Cu(1 1 1) surface for two different photoelectron kinetic energies. Differences and similarities between single and multiple scattering are discussed in comparison with experimental results. We find that the present approach gives very good results despite some limitations.
    Surface Science 01/2006; · 1.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Full hemispherical X-ray photoelectron diffraction (XPD) experiments have been performed to investigate at the atomic level ultrathin epitaxial c-axis oriented PbTiO 3 (PTO) films grown on Nb-doped SrTiO 3 substrates. Comparison between experiment and theory allows us to identify a preferential ferroelectric polarization state in a 60 Å -thick PTO film. Multiple scattering theory based on a cluster-model [ Phys. Rev. B $\textbf{63}$ , 075404 (2001)] is used to simulate the experiments. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006
    Physics of Condensed Matter 01/2006; 49(2):141-146. · 1.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: X-ray photoelectron diffraction is used to directly probe the intra-cell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab-initio calculations, unambiguously demonstrate non-centro-symmetry in films a few unit cells thick, imply that films as thin as 3 unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface.
    Physical Review B 11/2005; · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Quantum well states are a consequence of confinement in a quantum cavity. In this study we investigate with photoemission the influence of the interface electronic structure on the quantum well state energy dispersion in ultrathin Mg(0001) films on W(110). Coupling between the sp-derived quantum well states and the substrate across the interface becomes manifest in a deviation from free electronlike dispersion behavior. Most importantly, we observe a marked level splitting, which is interpreted as due to the Rashba effect at the interface. Such an interfacial electron beam splitting on materials with strong spin-orbit coupling is an essential ingredient for novel spintronic devices. The combination of a quantum cavity with a heavy, electron reflecting substrate reveals spin-splitting effects in ultrathin films without conventional magnetism being involved.
    Physical Review Letters 10/2005; 95(12):126401. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The origin of the monoclinic distortion and domain formation in the quasi-two-dimensional layer compound NbTe2 is investigated. Angle-resolved photoemission shows that the Fermi surface is pseudogapped over large portions of the Brillouin zone. Ab initio calculation of the electron and phonon band structure as well as the static RPA susceptibility lead us to conclude that Fermi surface nesting and electron-phonon coupling play a key role in the lowering of the crystal symmetry and in the formation of the charge density wave phase.
    Physical review. B, Condensed matter 01/2005; 72(19). · 3.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report high-resolution angle-resolved photoemission experiments on epitaxial thin films of different rare-earth (RE) dihydrides (RE=Gd,La) and of YH2 and ScH2. It is found through ab initio calculations and confirmed by Fermi surface mapping that the electronic structure becomes very similar upon hydrogenation, rendering the studied dihydrides isoelectronic. We propose that the dihydride phase acts as a common precursor state for the formation of the insulating trihydride phase. For states with higher binding energies (which exhibit considerable H character) the agreement between calculation and measurement is less convincing. Independent of the difficulties to describe these hydrogen related states, we note in the comparison between experiment and calculation a very convincing description of the Fermi surface for the dihydrides. Therefore we trace the apparent inability of density, functional theory to describe the hygrogenation up to the trihydride phase to an insufficient description of hydrogen states in general and, in particular, involving octahedral sites.
    Physical Review B 10/2004; 70(16). · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We perform angle-resolved photoemission spectroscopy on 1T-TaS2 and 1T-TaSe2 using synchrotron radiation. We observe a characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions. Density functional theory calculation and group theory strongly suggest that this splitting is due to spin–orbit interaction along one direction, and to symmetry along the other direction. We note that, according to the Kramers degeneracy, the spin–orbit interaction leaves every state doubly degenerate. Furthermore, this study allows us to identify a mixing between bands with Ta 5d and Se 4p character, possibly relevant for the different temperature behaviours of the two compounds.
    Journal of Physics Condensed Matter 04/2004; 16(18):3271. · 2.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The transition metal dichalcogenide 1T-TaS2 is a layered material exhibiting charge density waves. Based on angle-resolved photoemission experiments mapping spectral weight at the Fermi surface and density functional theory calculations we discuss possible mechanisms involved with the creation of charge density waves. At first the flat parts of the elliptically shaped Fermi surface appear to play an important role via Fermi surface nesting. A closer analysis of the charge density wave induced new Brillouin zones and the possible energy balance between elastic deformation energy and electronic energy points to a more complicated scenario.
    Physica B Condensed Matter 01/2004; 351(3):245-249. · 1.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic ordering of the first row transition metal intercalates of NbS 2 due to coupling between the conduction electrons and the intercalated ions has been explained in terms of Fermi surface nesting. We use angle-resolved photoelectron spectroscopy to investigate the Fermi surface topology and the valence band structure of the quasi-two-dimensional layer compounds Mn 1/3 NbS 2 and Ni 1/3 NbS 2 . Charge transfer from the intercalant species to the host layer leads to non-uniform, pocket selective doping of the Fermi surface. The implication of our results on the nesting properties are discussed. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007
    Physics of Condensed Matter 57(4):385-390. · 1.28 Impact Factor