Valerio Olevano

Institut Néel, Grenoble, Rhône-Alpes, France

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Publications (67)189.41 Total impact

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    ABSTRACT: A Comment on the Letter by M. Calandra and F. Mauri Phys. Rev. Lett. 106 196406 (2011) The authors of the Letter offer a Reply.
    Physical Review Letters 01/2014; 112(4):049701. · 7.94 Impact Factor
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    ABSTRACT: We present two possible approaches to calculate the momentum distribution n(p) and the Compton profile within the framework of the ab initio GW approximation on the self-energy. The approaches are based on integration of the Green's function along either the real or the imaginary axes. Examples will be presented on the jellium model and on real bulk sodium. Advantages and drawbacks of both methods are discussed in comparison with accurate quantum Monte Carlo (QMC) calculations and x-ray Compton scattering experiments. We illustrate the effect of many-body correlations and disentangle them from band-structure and anisotropy effects by a comparison with density functional theory in the local density approximation. Our results suggest the use of G0W0 momentum distributions as reference for future experiments and theory developments.
    Physical review. B, Condensed matter 10/2012; 86(19).
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    ABSTRACT: Within the framework of ab initio time-dependent density-functional theory (TD-DFT), we propose a static approximation to the exchange-correlation kernel based on the jellium-with-gap model. This kernel accounts for electron-hole interactions and it is able to address both strongly bound excitons and weak excitonic effects. TD-DFT absorption spectra of several bulk materials (both semiconductor and insulators) are reproduced in very good agreement with the experiments and with a low computational cost.
    Physical review. B, Condensed matter 10/2012; 87(20).
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    ABSTRACT: The band structure of gold is calculated using ab initio many-body perturbation theory. Different approximations within the GW approach are considered. Standard single-shot G0W0 corrections modify the sp-like bands while leaving unchanged the 5d occupied bands. Beyond G0W0, quasiparticle self-consistency on the wave functions lowers the 5d bands. Globally, many-body effects achieve an opening of the 5d-6sp interband gap of ∼0.4 to ∼0.8 eV, reducing the discrepancy with the experiment. Finally, the quasiparticle band structure is compared to the one obtained by the widely used HSE (Heyd, Scuseria, and Ernzerhof) hybrid functional.
    Physical review. B, Condensed matter 03/2012; 86(12).
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    ABSTRACT: Cited By (since 1996): 1, Export Date: 22 November 2012, Source: Scopus, Art. No.: 195111, CODEN: PRBMD, doi: 10.1103/PhysRevB.85.195111, Language of Original Document: English, Correspondence Address: Cazzaniga, M.; Università Degli Studi di Milano, Physics Department, Milano, Italy, References: Mott, N.F., (1961) Philos. Mag., 6, p. 287. , 1478-6435 10.1080/14786436108243318;
    Physical Review B - Condensed Matter and Materials Physics. 01/2012; 85(19).
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    ABSTRACT: We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopymeasurements on TiSe2. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a approximate to 0.2- eV band-gap insulator consistent with our STS spectra at 5 K. The highest valence and the lowest conduction bands are strongly renormalized, with a loss of k(2) parabolic dispersion toward a k(4) shape. In particular, GW moves the top of valence moved toward a circle of points away from Gamma, arising in a Mexican hat shape commonly associated with an excitonic insulator. Our calculations are in good agreement with experiment.
    Physical Review B 01/2012; 85(19). · 3.77 Impact Factor
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    ABSTRACT: We calculate the off-diagonal density matrix of the homogeneous electron gas at zero temperature using unbiased reptation Monte Carlo calculations for various densities and extrapolate the momentum distribution and the kinetic and potential energies to the thermodynamic limit. Our results on the renormalization factor allow us to validate approximate G0W0 calculations concerning quasiparticle properties over a broad density region (1≤r(s)≲10) and show that, near the Fermi surface, vertex corrections and self-consistency aspects almost cancel each other out.
    Physical Review Letters 09/2011; 107(11):110402. · 7.94 Impact Factor
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    ABSTRACT: We present both theoretical ab initio GW and experimental angle-resolved photoemission (ARPES) and scanning tunneling (STS) spectroscopy results on TiSe2. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a ~ 0.2 eV band gap insulator consistent with our STS spectra at 5 K. The band shape is strongly renormalized, with the top-of-valence moved towards a circle of points away from \Gamma, arising in a mexican hat feature typical of an excitonic insulator. Our calculations are in good agreement with experiment.
    03/2011;
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    ABSTRACT: The conductance of single molecule junctions is calculated using a Landauer approach combined to many-body perturbation theory MBPT) to account for electron correlation. The mere correction of the density-functional theory eigenvalues, which is the standard procedure for quasiparticle calculations within MBPT, is found not to affect noticeably the zero-bias conductance. To reduce it and so improve the agreement with the experiments, the wavefunctions also need to be updated by including the non-diagonal elements of the self-energy operator.
    Physical review. B, Condensed matter 02/2011; 84.
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    ABSTRACT: We investigate some aspects of the self-consistency in the Dyson-Schwinger approach to both the QED and the self-interacting scalar field theories. We prove that the set of the Dyson-Schwinger equations, together with the Green-Ward-Takahashi identity, is equivalent to the analogous set of integral equations studied in condensed matter, namely, many-body perturbation theory, where it is solved self-consistently and iteratively. In this framework, we compute the nonperturbative solution of the gap equation for the self-interacting scalar field theory.
    Physical review D: Particles and fields 11/2010; 82(9).
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    ABSTRACT: We present experimental and theoretical results on the momentum distribution and the quasiparticle renormalization factor in sodium. From an x-ray Compton-profile measurement of the valence-electron-momentum density, we derive its discontinuity at the Fermi wave vector. This yields an accurate measure of the renormalization factor that we compare with quantum Monte Carlo and G0W0 calculations performed both on crystalline sodium and on the homogeneous electron gas.
    Physical Review Letters 08/2010; 105(8):086403. · 7.94 Impact Factor
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    ABSTRACT: We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7−δ. The response of the low-lying Ba 5p and Y 4p core electrons is shown to interact strongly with the Cu 3d and O 2p excitations, with important consequences on screening. The agreement between IXS and TDDFT results is excellent, apart from a new type of excitations, mainly related to loosely bound Ba electrons and significantly affected by correlations. This points to correlation mechanisms not fully described by TDDFT that might have a role in giving rise to antiscreening.
    Phys. Rev. B. 08/2010; 82(6).
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    Valerio Olevano, Massimo Ladisa
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    ABSTRACT: We present a relativistic covariant form of many-body theory. The many-body covariant Lagrangian is derived from QED by integrating out the internal non-quantized electromagnetic field. The ordinary many-body Hamiltonian is recovered as an approximation to the exact covariant theory that contains many-body terms beyond the solely electrostatic interaction, e.g. the Lorentz force among electrons, spin-spin etc. Spin and relativistic terms, e.g. spin-orbit, are also automatically accounted. Moreover, the theory is compact, gauge-invariant and respects causality. Comment: Secondary subj-class: hep-ph
    02/2010;
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    ABSTRACT: We present ab initio many-body calculations of the optical absorption in bulk graphite, graphene and bilayer of graphene. Electron-hole interaction is included solving the Bethe-Salpeter equation on top of a GW quasiparticle electronic structure. For all three systems, we observe strong excitonic effects at high energy, well beyond the continuum of pi-->pi* transitions. In graphite, these affect the onset of sigma-->sigma* transitions. In graphene, we predict an excitonic resonance at 8.3 eV arising from a background continuum of dipole forbidden transitions. In the graphene bilayer, the resonance is shifted to 9.6 eV. Our results for graphite are in good agreement with experiments.
    Physical review. B, Condensed matter 01/2010; 81(12).
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    ABSTRACT: We present a detailed investigation of the dynamic structure factor S(Q,ω) as well as of the dielectric function εM(Q,ω) of the prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering measurements and ab initio calculations. We show that, in contrast to optical spectra, for finite momentum transfer, time-dependent density-functional theory in adiabatic local-density approximation (TDLDA) together with the inclusion of lifetime effects in a modified independent-particle polarizability χ0,LT describes the physics of valence excitations with high precision. This applies to the dynamic structure factor as well as to the dielectric function, which demonstrates that TDLDA contains the short-range many-body effects that are crucial for a correct description of εM(Q,ω) in silicon at finite momentum transfer. The form of a nonlocal and energy-dependent exchange-correlation kernel is presented which provides the inclusion of the lifetime effects using the true independent-particle polarizability χ0. The description of the silicon L2,3 absorption edge has been possible by including the outer core electrons 2s and 2p in the valence electrons of the pseudopotential. The energy of the edge is underestimated but a scissor shift of the respective states by the self-energy correction for these states yields good agreement with experiment. Short-range crystal local-field effects and exchange-correlation effects become important with increasing momentum transfer. The inclusion of crystal local-field effects in the random-phase approximation is able to describe the anisotropy of the response well. Our results demonstrate the quantitative predictive power of the first-principles description.
    Physical review. B, Condensed matter 01/2010; 81(8).
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    ABSTRACT: It has been known for almost 25 years that high temperature treatment of polar faces of SiC crystals lead to the graphitisation of the surface as a consequence of Si preferential sublimation. The group of Walt de Heer in Atlanta has proposed to use this procedure to obtain macroscopic multilayer graphene samples. This has lead to a renewal of interest for the study of the graphitic layers grown on the SiC surfaces. Due to the polar nature of the material, the 6H(4H)-SiC substrate present two non-equivalent surfaces: the (0001) is known as the Si face, and the (000-1) one is the C face. It turns out that the structure and the properties of the multilayer graphene samples obtained on those two surfaces are rather different. In particular the multilayer graphene samples grown on the C-terminated face presents electronic properties that are rather similar to those of monolayer graphene with very high mobility. This is shown by transport and optical experiments under high magnetic field. This surprising result is explained by the rotational stacking sequence, observed experimentally. which leads to an electronic decoupling as demonstrated by ab initio band structure calculations.
    Int. J. Nanotechnol. 01/2010; 7.
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    ABSTRACT: We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7-delta . The response of the low-lying Ba5p and Y4p core electrons is shown to interact strongly with the Cu3d and O2p excitations, with important consequences on screening. The agreement between IXS and TDDFT results is excellent, apart from a new type of excitations, mainly related to loosely bound Ba electrons and significantly affected by correlations. This points to correlation mechanisms not fully described by TDDFT that might have a role in giving rise to antiscreening.
    Physical Review B 01/2010; 82(6):064514. · 3.77 Impact Factor
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    Pierre Darancet, Valerio Olevano, Didier Mayou
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    ABSTRACT: We introduce a quantum transport formalism based on a map of a real three-dimensional lead-conductor-lead system into an effective one-dimensional (1D) system. The resulting effective 1D theory is an in principle exact formalism to calculate the conductance. Besides being more efficient than the principal layers approach, it naturally leads to a five-partitioned workbench (instead of three) where each part of the device (the true central device, the ballistic and the nonballistic leads) is explicitely treated, allowing better physical insight into the contact resistance mechanisms. Independently, we derive a generalized Fisher-Lee formula and a generalized Meir-Wingreen formula for the correlated and uncorrelated conductance and current of the system where the initial restrictions to ballistic leads are generalized to the case of resistive contacts. We present an application to graphene nanoribbons.
    Physical review. B, Condensed matter 01/2010; 81(15).
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    Pierre Darancet, Valerio Olevano, Didier Mayou
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    ABSTRACT: Nanoelectronic devices smaller than the electron wavelength can be achieved in graphene with current lithography techniques. Here we show that the electronic quantum transport of graphene subwavelength nanodevices presents deep analogies with subwavelength optics. We introduce the concept of electronic diffraction barrier to represent the effect of constrictions and the rich transport phenomena of a variety of nanodevices. Results are presented for Bethe and Kirchhoff diffraction in graphene slits and Fabry-Perot interference oscillations in nanoribbons. The same concept applies to graphene quantum dots and gives new insight into recent experiments in these systems.
    Physical Review Letters 05/2009; 102(13):136803. · 7.94 Impact Factor
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    ABSTRACT: A method is presented which is able to interpolate between spectra depending parametrically on one variable and obeying a sum rule. This enables the description of experiments with a finite resolution in that parameter because integrals over certain parameter ranges are easily obtained, as for instance in the case of inelastic x-ray scattering with finite resolution in momentum transfer. Beyond the sum rule, the method does not use further assumptions about the physics of the system. It is applicable to a wide range of spectra as for instance the dynamic structure factor or the dielectric function for different moduli or directions of momentum transfer, absorption spectra for different alloy compositions or for a range of nanocrystal sizes, probability distributions, etc. The method is expected to be useful not only in the simulation of experimental spectra but also in calculations where the determination of certain spectral quantities is numerically cumbersome. A code carrying out the interpolation is provided.
    Physical review. B, Condensed matter 01/2009; 79(9).

Publication Stats

788 Citations
189.41 Total Impact Points

Institutions

  • 2008–2012
    • Institut Néel
      Grenoble, Rhône-Alpes, France
    • École Polytechnique
      Paliseau, Île-de-France, France
  • 2010
    • European Synchrotron Radiation Facility
      Grenoble, Rhône-Alpes, France
  • 2008–2010
    • University Joseph Fourier - Grenoble 1
      • Institut Néel
      Grenoble, Rhone-Alpes, France
  • 2005–2010
    • French National Centre for Scientific Research
      • Institut Néel
      Lutetia Parisorum, Île-de-France, France
  • 2004
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 1999–2000
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy