Publications by authors named "Felix Yndurain"

12 Publications

  • Page 1 of 1

Critical analysis of the response function in low dimensional materials.

J Phys Condens Matter 2021 Feb 26. Epub 2021 Feb 26.

Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, Madrid, 28049, SPAIN.

The presence of sharp peaks in the real part of the static dielectric response function are usually accepted as indication of charge or spin instabilities in a material. However, there are misconceptions that Fermi surface (FS) nesting guarantees a peak in the response function like in one-dimensional systems, and, in addition, response function matrix elements between empty and occupied states are usually considered of secondary importance and typically set to unity like in the free electron gas case. In this work, we explicitly show, through model systems and real materials, within the framework of density functional theory, that predictions about the peaks in the response function, using FS nesting and constant matrix elements yields erroneous conclusions. We find that the inclusion of the matrix elements completely alters the structure of the response function. In all the cases studied other than the one-dimensional case we find that the inclusion of matrix elements washes out the structure found with constant matrix elements. Our conclusion is that it is imperative to calculate the full response function, with matrix elements, when making predictions about instabilities in novel materials.
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http://dx.doi.org/10.1088/1361-648X/abea41DOI Listing
February 2021

Band unfolding made simple.

J Phys Condens Matter 2020 May;32(20):205902

Departamento e Instituto de Física de la Materia Condensada (IFIMAC), Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.

We present a simple view on band unfolding of the energy bands obtained from supercell calculations. It relies on the relationship between the local density of states in reciprocal space and the fully unfolded band structure. This provides an intuitive and valid approach not only for periodic, but also for systems with no translational symmetry. By refolding into the primitive Brillouin zone of the pristine crystal we recover the conventional unfolded bands. We implement our algorithm in the Siesta package. As an application, we study a set of benchmark examples, ranging from simple defects on crystals to systems with increasing complexity and of current interest, as the effect of external pressure on rotated graphene bilayers.
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http://dx.doi.org/10.1088/1361-648X/ab6e8eDOI Listing
May 2020

Organometallic MTCNQ films: a comparative study of CuTCNQ versus AgTCNQ.

Phys Chem Chem Phys 2018 Aug;20(33):21705-21715

Instituto de Estructura de la Materia, CSIC, c/Serrano 119, 28006 Madrid, Spain.

We performed a systematic study of electron-acceptor molecules in two closely related organometallic solids, namely, CuTCNQ and AgTCNQ. These studies were performed using both an experimental approach, via the use of electron spectroscopies (XPS and UPS), and a theoretical approach, via the use of ab initio DFT calculations. From these results, a complete description of the electronic structure of these molecular solid-films could be given, identifying the characteristic electronic and structural features of each part of the molecules and their contribution to the final electronic structure. Empty states were found close to the Fermi level in both solids. The presence of an electronic band close to the Fermi level is related to the magnetic behavior predicted for both MTCNQ solids for their isolated monolayers. However, the lower work function of the MTCNQ with respect to the metal substrate one implies that the MTCNQ film accepts electron from the metal substrate, thus fulfilling its Fermi level band. This occupied band explains the absence of shake-up features in the core level spectra in opposition to the TCNQ. The UPS experiments indicated that the MTCNQ film was doped by a small excess of metal from the substrate, shifting the electron Fermi level close to the MTCNQ conduction band. Thus, the MTCNQ film becomes an n-type semiconductor, opening up a very interesting field in the technological applications of this system.
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http://dx.doi.org/10.1039/c8cp02438cDOI Listing
August 2018

Selective Hydrogen Adsorption in Graphene Rotated Bilayers.

J Phys Chem B 2018 01 9;122(2):595-600. Epub 2017 Aug 9.

Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid , Cantoblanco, 28049 Madrid, Spain.

The absorption energy of atomic hydrogen at rotated graphene bilayers is studied using ab initio methods based on the density functional theory including van der Waals interactions. We find that, due to the surface corrugation induced by the underneath rotated layer and the perturbation of the electronic density of states near the Fermi energy, the atoms with an almost AA stacking are the preferential ones for hydrogen chemisorption. The adsorption energy difference between different atoms can be as large as 80 meV. In addition, we find that, due to the logarithmic van Hove singularities in the electronic density of states at energies close to the Dirac point, the adsorption energy of either electron or hole doped samples is substantially increased. We also find that the adsorption energy increases with the decrease of the rotated angle between the layers. Finally, the large zero point energy of the C-H bond (∼0.3 eV) suggests adsorption and desorption of atomic hydrogen and deuterium should behave differently.
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http://dx.doi.org/10.1021/acs.jpcb.7b05085DOI Listing
January 2018

Atomic-scale control of graphene magnetism by using hydrogen atoms.

Science 2016 Apr;352(6284):437-41

Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain. Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain. Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid, Spain.

Isolated hydrogen atoms absorbed on graphene are predicted to induce magnetic moments. Here we demonstrate that the adsorption of a single hydrogen atom on graphene induces a magnetic moment characterized by a ~20-millielectron volt spin-split state at the Fermi energy. Our scanning tunneling microscopy (STM) experiments, complemented by first-principles calculations, show that such a spin-polarized state is essentially localized on the carbon sublattice opposite to the one where the hydrogen atom is chemisorbed. This atomically modulated spin texture, which extends several nanometers away from the hydrogen atom, drives the direct coupling between the magnetic moments at unusually long distances. By using the STM tip to manipulate hydrogen atoms with atomic precision, it is possible to tailor the magnetism of selected graphene regions.
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http://dx.doi.org/10.1126/science.aad8038DOI Listing
April 2016

Magnetism in nanoparticles: tuning properties with coatings.

J Phys Condens Matter 2013 Dec;25(48):484006

This paper reviews the effect of organic and inorganic coatings on magnetic nanoparticles. The ferromagnetic-like behaviour observed in nanoparticles constituted by materials which are non-magnetic in bulk is analysed for two cases: (a) Pd and Pt nanoparticles, formed by substances close to the onset of ferromagnetism, and (b) Au and ZnO nanoparticles, which were found to be surprisingly magnetic at the nanoscale when coated by organic surfactants. An overview of theories accounting for this unexpected magnetism, induced by the nanosize influence, is presented. In addition, the effect of coating magnetic nanoparticles with biocompatible metals, oxides or organic molecules is also reviewed, focusing on their applications.
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http://dx.doi.org/10.1088/0953-8984/25/48/484006DOI Listing
December 2013

Stability, adsorption, and diffusion of CH₄, CO₂, and H₂ in clathrate hydrates.

Phys Rev Lett 2010 Oct 28;105(14):145901. Epub 2010 Sep 28.

Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.

We present a study of the adsorption and diffusion of CH₄, CO₂, and H₂ molecules in clathrate hydrates using ab initio van der Waals density functional formalism [M. Dion, Phys. Rev. Lett. 92, 246401 (2004)10.1103/PhysRevLett.92.246401]. We find that the adsorption energy is dominated by van der Waals interactions and that, without them, gas hydrates would not be stable. We calculate the maximum adsorption capacity as well as the maximum hydrocarbon size that can be adsorbed. The relaxation of the host lattice is essential for a good description of the diffusion activation energies, which are estimated to be of the order of 0.2, 0.4, and 1.0 eV for H₂, CO₂, and CH₄, respectively.
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http://dx.doi.org/10.1103/PhysRevLett.105.145901DOI Listing
October 2010

First principles calculation of localized surface phonons and electron-phonon interaction at pb(111) thin films.

Phys Rev Lett 2008 May 21;100(20):205501. Epub 2008 May 21.

Departamento de Física de la Materia Condensada and Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.

A first principles calculation of the vibrational modes of Pb(111) thin films of thickness up to 14 layers reveals the existence of localized vibrational modes at the slab's surface. Both longitudinal and transverse surface modes localized a few atomic layers are found at energies above the bulk bands. The frequency of these modes presents a bilayer oscillatory behavior. The electron-phonon interaction of the slab's quantum well states is also calculated. We find a large (small) deformation potential for the lowest unoccupied (highest occupied) quantum well state. Its absolute value is also oscillatory with the number of layers.
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http://dx.doi.org/10.1103/PhysRevLett.100.205501DOI Listing
May 2008

Superconductivity and magnetic order in CeRhIn5: spectra of coexistence.

Phys Rev Lett 2007 Mar 22;98(12):126406. Epub 2007 Mar 22.

Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain.

We discuss the fixed-point Hamiltonian and the spectrum of excitations of a quasi-bidimensional electronic system supporting simultaneously antiferromagnetic ordering and superconductivity. The coexistence of these two order parameters in a single phase is possible because the magnetic order is linked to the formation of a metallic spin density wave, and its order parameter is not associated to a spectral gap but to an energy shift of the paramagnetic bands. This peculiarity entails several distinct features in the phase diagram and the spectral properties of the model, which may have been observed in CeRhIn5. Apart from the coexistence, we find an abrupt suppression of the spin density wave when the superconducting and magnetic ordering temperatures are equal. The divergence of the cyclotron mass extracted from de Haas-van Alphen experiments is also analyzed in the same framework.
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http://dx.doi.org/10.1103/PhysRevLett.98.126406DOI Listing
March 2007

Formation of gold nanowires with impurities: a first-principles molecular dynamics simulation.

Phys Rev Lett 2007 Mar 27;98(9):096102. Epub 2007 Feb 27.

Departamento de Física de la Materia Condensada, C-III, Universidad Autónoma de Madrid, E-28049 Madrid, Spain.

We present first-principles molecular dynamics simulations of the formation of monatomic gold nanowires with different impurities (H, C, O, S). Special care was taken not to bias the probability that the impurity atoms participate in the monatomic wire, which is the main focus of this work. Hydrogen always evaporated before the formation of the monatomic chains. Carbon and oxygen were found in the final chains with low probability ( approximately 10%), while sulfur almost always participated in it (probabability approximately 90%). The mean distances between gold atoms bridged by carbon, oxygen, and sulfur were 3.3, 4.4, and 5.0 A, respectively, in good agreement with experimental observations. The contributions of carbon, oxygen, and sulfur to the density of electronic states at the Fermi level are neglegible, moderate, and large, respectively.
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http://dx.doi.org/10.1103/PhysRevLett.98.096102DOI Listing
March 2007

Comment on "Magnetism in atomic-size palladium contacts and nanowires".

Phys Rev Lett 2006 Feb 22;96(7):079701; author reply 079702. Epub 2006 Feb 22.

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http://dx.doi.org/10.1103/PhysRevLett.96.079701DOI Listing
February 2006

1D lattice distortions as the origin of the (2 x 2)p4gm reconstruction in gamma'-Fe4N(100): a magnetism-induced surface reconstruction.

Phys Rev Lett 2005 Sep 20;95(13):136102. Epub 2005 Sep 20.

Instituto de Ciencia de Materiales de Madrid-CSIC, Cantoblanco, 28049-Madrid, Spain.

The (100) surface of magnetic gamma'-Fe4N films epitaxially grown on Cu(100) shows a (2 x 2)p4gm reconstruction. The atom positions determined experimentally are properly accounted for by first-principles total energy calculations, which further reveal that the (2 x 2)p4gm reconstruction requires the topmost Fe4N2 plane to be magnetic and effectively decoupled from the rest of the crystal and that it originates from the perpendicular crossing of one-dimensionally dimerized Fe chains.
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http://dx.doi.org/10.1103/PhysRevLett.95.136102DOI Listing
September 2005