Instituto Madrileno Of Estudios Avanzados En Nanociencia

Madrid, Spain

Instituto Madrileno Of Estudios Avanzados En Nanociencia

Madrid, Spain

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Yip F.L.,Autonomous University of Madrid | Rescigno T.N.,Lawrence Berkeley National Laboratory | McCurdy C.W.,Lawrence Berkeley National Laboratory | McCurdy C.W.,University of California at Davis | And 2 more authors.
Physical Review Letters | Year: 2013

Triply differential cross sections are calculated for one-photon double ionization of neon and argon at various photon energies and electron energy sharings by using a frozen-core treatment to represent the remaining electrons of the residual ion. Angular distributions agree well with all existing experimental data, showing that in spite of its simplicity the method can treat the double ionization of complex targets reliably. A comparison of the cross sections for helium, neon, and argon into the same final state symmetry at the same relative excess energies reveals a distinctive signature of the role of electron correlation in each target. © 2013 American Physical Society.


Calleja F.,Instituto Madrileno Of Estudios Avanzados En Nanociencia | Ochoa H.,CSIC - Institute of Materials Science | Garnica M.,Instituto Madrileno Of Estudios Avanzados En Nanociencia | Garnica M.,Autonomous University of Madrid | And 14 more authors.
Nature Physics | Year: 2015

The electronic band structure of a material can acquire interesting topological properties in the presence of a magnetic field or as a result of the spin-orbit coupling. We study graphene on Ir, with Pb monolayer islands intercalated between the graphene sheet and the Ir surface. Although the graphene layer is structurally unaffected by the presence of the Pb islands, its electronic properties change markedly, with regularly spaced resonances appearing. We interpret these resonances as the effect of a strong and spatially modulated spin-orbit coupling, induced in graphene by the Pb monolayer. As well as confined electronic states, the electronic spectrum has a series of gaps with non-trivial topological properties, resembling a realization of the quantum spin Hall effect proposed by Bernevig and Zhang. © 2014 Macmillan Publishers Limited. All rights reserved.


Arias-Gonzalez J.R.,Instituto Madrileno Of Estudios Avanzados En Nanociencia | Arias-Gonzalez J.R.,CSIC - National Center for Biotechnology
PLoS ONE | Year: 2012

Information has an entropic character which can be analyzed within the framework of the Statistical Theory in molecular systems. R. Landauer and C.H. Bennett showed that a logical copy can be carried out in the limit of no dissipation if the computation is performed sufficiently slowly. Structural and recent single-molecule assays have provided dynamic details of polymerase machinery with insight into information processing. Here, we introduce a rigorous characterization of Shannon Information in biomolecular systems and apply it to DNA replication in the limit of no dissipation. Specifically, we devise an equilibrium pathway in DNA replication to determine the entropy generated in copying the information from a DNA template in the absence of friction. Both the initial state, the free nucleotides randomly distributed in certain concentrations, and the final state, a polymerized strand, are mesoscopic equilibrium states for the nucleotide distribution. We use empirical stacking free energies to calculate the probabilities of incorporation of the nucleotides. The copied strand is, to first order of approximation, a state of independent and non-indentically distributed random variables for which the nucleotide that is incorporated by the polymerase at each step is dictated by the template strand, and to second order of approximation, a state of non-uniformly distributed random variables with nearest-neighbor interactions for which the recognition of secondary structure by the polymerase in the resultant double-stranded polymer determines the entropy of the replicated strand. Two incorporation mechanisms arise naturally and their biological meanings are explained. It is known that replication occurs far from equilibrium and therefore the Shannon entropy here derived represents an upper bound for replication to take place. Likewise, this entropy sets a universal lower bound for the copying fidelity in replication. © 2012 J. Ricurdo Arias-Gonzalez.


Silva R.E.F.,Autonomous University of Madrid | Catoire F.,University of Bordeaux 1 | Riviere P.,Autonomous University of Madrid | Bachau H.,University of Bordeaux 1 | And 2 more authors.
Physical Review Letters | Year: 2013

We present a theoretical study of H2+ ionization under strong IR femtosecond pulses by using a method designed to extract correlated (2D) photoelectron and proton kinetic energy spectra. The results show two distinct ionization mechanisms - tunnel and multiphoton ionization - in which electrons and nuclei do not share the energy from the field in the same way. Electrons produced in multiphoton ionization share part of their energy with the nuclei, an effect that shows up in the 2D spectra in the form of energy-conservation fringes similar to those observed in weak-field ionization of diatomic molecules. In contrast, tunneling electrons lead to fringes whose position does not depend on the proton kinetic energy. At high intensity, the two processes coexist and the 2D plots show a very rich behavior, suggesting that the correlation between electron and nuclear dynamics in strong field ionization is more complex than one would have anticipated. © 2013 American Physical Society.


Catoire F.,University of Bordeaux 1 | Silva R.E.F.,Autonomous University of Madrid | Riviere P.,Autonomous University of Madrid | Bachau H.,University of Bordeaux 1 | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We present an extension of the resolvent-operator method (ROM), originally designed for atomic systems, to extract differential photoelectron spectra (in photoelectron- and nuclear-kinetic energy) for diatomic molecules interacting with strong, ultrashort laser fields in the single active electron approximation. The method is applied to the study of H2+ photodissociation and photoionization by femtosecond laser pulses in the XUV-IR frequency range. In particular, the method is tested (i) in the perturbative regime, for few-photon absorption and bound-bound electronic transitions, and (ii) in the strong-field regime, in which multiphoton absorption and tunneling are present. In the latter case, we show how the differential ROM allows one to track the transition between both regimes. We also analyze isotopic effects by comparing the dynamics of H2+ and D2+ ionization for different pulses. © 2014 American Physical Society.


Calegari F.,CNR Institute of Neuroscience | Ayuso D.,Autonomous University of Madrid | Trabattoni A.,Polytechnic of Milan | Belshaw L.,Queen's University of Belfast | And 11 more authors.
Science | Year: 2014

In the past decade, attosecond technology has opened up the investigation of ultrafast electronic processes in atoms, simple molecules, and solids. Here, we report the application of isolated attosecond pulses to prompt ionization of the amino acid phenylalanine and the subsequent detection of ultrafast dynamics on a sub-4.5-femtosecond temporal scale, which is shorter than the vibrational response of the molecule. The ability to initiate and observe such electronic dynamics in polyatomic molecules represents a crucial step forward in attosecond science, which is progressively moving toward the investigation of more and more complex systems.


Nandi S.,Tata Institute of Fundamental Research | Agnihotri A.N.,Tata Institute of Fundamental Research | Kasthurirangan S.,Institute of Chemical Technology | Kumar A.,Bhabha Atomic Research Center | And 5 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We have measured the absolute double-differential cross sections (DDCSs) for electron emission in ionization of O 2 molecules under the impact of 3.5-MeV/u C6 + ions. The data were collected between 10 and 600 eV, in an angular range of 30 - to 150 -. The single-differential cross sections (SDCSs) in emission angle and electron energy are deduced from the electron DDCS spectra. Also, the total cross section has been obtained from the SDCS spectra. The DDCS spectra as well as the SDCS spectra are compared with continuum distorted-wave eikonal initial-state calculations which employ molecular wave functions built as linear combinations of atomic orbitals. The DDCS ratio i.e. σ O 2/ 2σ O, derived by dividing the experimental DDCS for molecular oxygen with the theoretical DDCS for atomic oxygen, does not show any primary or secondary oscillations arising from Young-type interference, which is apparently in contrast to what has been observed earlier for H 2 and in agreement with the model calculation. Similarly, the forward-backward angular asymmetry increases monotonically with the velocity of the emitted electrons. However, the results on the DDCSs, SDCSs, the asymmetry parameter, and the nonexistence of oscillations are in qualitative agreement with the predictions of the model used. © 2012 American Physical Society.


Silva R.E.F.,Autonomous University of Madrid | Riviere P.,Autonomous University of Madrid | Martin F.,Autonomous University of Madrid | Martin F.,Instituto Madrileno Of Estudios Avanzados En Nanociencia
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We present a theoretical study of H 2 ionization by a pump-probe scheme consisting on an attosecond pulse train (APT) and a near-infrared (IR) pulse. We focus on the autoionization dynamics of the first series of resonant states of the molecule, the Q 1 doubly excited states. The APT central frequency is tuned to populate the 1Σu+ resonant states. The trace of autoionization is clearly visible in the two-dimensional (2D) proton-electron coincidence spectra and in the proton kinetic energy spectra. The dynamics of the autoionization process is clearly visible in the movie obtained by plotting the 2D spectrum as a function of the time delay between the APT and IR pulses. An analysis of the final symmetries Σ g and Σ u allows us to track the origin of the different structures. © 2012 American Physical Society.


Palacios A.,Autonomous University of Madrid | Feist J.,Harvard - Smithsonian Center for Astrophysics | Gonzalez-Castrillo A.,Autonomous University of Madrid | Sanz-Vicario J.L.,University of Antioquia | And 2 more authors.
ChemPhysChem | Year: 2013

Atomic autoionization following photoabsorption is a typical example of quantum interferences governed by electron-electron correlation. Coherence between direct photoionization and autoionization paths results in "Fano profiles", widely explored in atoms in the last 60 years. The advent of femto- and attosecond laser technology made time-resolved images of the delayed electron ejection in autoionization accessible, leading to the reemergence of such studies in atomic systems. The counterpart molecular phenomena show the richness, as well as the complexity, added by nuclear motion, which may proceed on similar time scales. However, Fano profiles are usually absent in measured molecular photoionization cross sections and an unequivocal parametrization of molecular autoionization signatures, similar to that introduced by Fano in atoms [U. Fano, Phys. Rev. 1961, 124, 1866] has not yet been achieved. In this work we introduce a simple semiclassical model that accounts for all the features observed in H2 photoionization and demonstrate that the interference structures observed in dissociative ionization spectra are almost exclusively due to the phase accumulated in the nuclear motion. Furthermore, we show that the temporal build-up of these structures in the energy-differential cross sections is also determined by nuclear motion. We validate our models by comparing with full-dimensional ab initio calculations solving the time-dependent Schrödinger equation. Simpler than you might think: A simple semiclassical model is introduced that accounts for all the features observed in H2 photoionization and demonstrate that the interference structures observed in dissociative ionization spectra are almost exclusively due to the phase accumulated in the nuclear motion. Furthermore, we show that the temporal build-up of these structures in the energy-differential cross sections is also determined by nuclear motion. We validate our models by comparing with full-dimensional ab initio calculations solving the time-dependent Schrdinger equation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Chang B.Y.,Seoul National University | Shin S.,Seoul National University | Palacios A.,Autonomous University of Madrid | Martin F.,Autonomous University of Madrid | And 2 more authors.
ChemPhysChem | Year: 2013

A laser-adiabatic manipulation of the bond (LAMB) scheme using moderately intense fields is proposed to induce and control large-amplitude oscillations in nuclear wave packets. The present scheme involves an ultrashort UV pump pulse to initially create a wave packet in an excited electronic state of the hydrogen molecular ion and a low-frequency control pulse, which is switched on after a given time, leading to controllable vibrational trapping. The choice of H 2 + as the target exploits the larger dipole values that molecular ions present as the internuclear distance increases. The amplitude and oscillation period of the wave packet is tuned by the field parameters of the control pulse, and more importantly, significant dissociation and ionization losses are prevented by keeping the laser intensities below hundreds of Terawatts. Our numerical simulations, based on the solution of the time-dependent Schrödinger equation, show that this control of the bond length is achieved in a wide range of moderate intensities and for relatively long pulse durations, from tens to hundreds of femtoseconds. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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