Suchergebnisse

Para una adecuada conducción de la política monetaria en una economía pequeña y abierta como la colombiana, debe tenerse en cuenta tanto el trilema de la política monetaria, como el ancla nominal de la economía. En este contexto, el papel del banco central es el de decidir cuál es el ancla nominal para la economía. Sin embargo, existe simultáneamente una estrecha relación entre la política monetaria y la brecha del producto. El objetivo de este estudio es ilustrar esta dinámica a través de un modelo de política monetaria. Los resultados muestran la relación dinámica entre el comportamiento de la tasa de interés como función de la inflación subyacente y la brecha del producto. Una de las principales características de la solución es que la restricción de no negatividad sobre la tasa de interés es obligatoria para bajos niveles de brecha del producto y bajas tasas de inflación ; To develops an adequate an monetary policy, in a small open economy like the Colombian, must take in to account, the Trilema of monetary policy and the nominal anchor of the economy, in this context, the central bank role is that the decide which is the nominal anchor to the economy, however exist simultaneously a close relationship between the monetary policy and the gross domestic product gap, the goal of this study is to illustrate this dynamic thought of an monetary policy model, the results show that the behavior of an optimal interest rate like a function of the subjacent inflation and the gross domestic product gap, one of the principal characteristics of the solutions is that the restrictions of no negativity over the interest rate is necessary to lowers levels of gross domestic product gap and lowers rates of inflation

Understanding the mechanism of molecular dissociation under applied bias is a fundamental requirement to progress in (electro)-catalysis as well as in (opto)-electronics. The working conditions of a molecular-based device and the stability of chemical bonds can be addressed in metal–organic junctions by injecting electrons in tunneling conditions. Here, we have correlated the energy of de-bromination of an aryl group with its density of states in a self-assembled dimeric structure of 4′-bromo-4-mercaptobiphenyl adsorbed on a Au(111) surface. We have observed that the electron-energy range where the molecule is chemically stable can be extended, shifting the bias threshold for the rupture of the –C–Br bond continuously from about 2.4 to 4.4 V by changing the electron current. Correspondingly, the power needed for the dissociation drops sharply at 3.6 V, identifying different reaction regimes and the contribution of different molecular resonance states. ; A.B. acknowledges Vicerrectorado de Investigacion of the University of the Basque Country (UPV/EHU) for the PhD fellowship (2016). R.R. and N.L. are grateful for the computer resources at Finisterrae II, the technical support provided by CESGA and the EU-FET Open H2020 Mechanics with Molecules project (grant 766864). A.B. and L.V. acknowledge the funding of Spanish Ministry of Economy, Industry and Competitiveness (MINECO Grant number MAT2016-78293-C6-5-R); Diputacion Foral de Guipuzcoa (Red/Sarea 2020-CIEN-000009-01), and the Basque Government (Proyectos de Investigación Básica y/o Aplicada grant number PIBA-2021-0026). ; Peer reviewed

The transition rule governing the inelastic excitations of molecular vibrations occurring during a molecular through-state electron transfer process is presented. Using an effective Hamiltonian model, it is shown that the quantum time oscillation of the intermediate electronic state population triggers this transition. Its corresponding quantum oscillation frequency has to be equal to a quantum of vibration. This transition rule is extended to the full spectrum of a quantum vibrator. This new transition rule is expected to be robust when electronically coupling the molecule to the metallic pads of a voltage-biased tunnel junction. © 2013 Elsevier B.V. All rights reserved. ; This work has been supported by the ICT-FET European Union Integrated Project AtMol (http://www.atmol.eu). ; Peer Reviewed

arXiv:1806.02999v1 ; Enhancing the spin–orbit interaction in graphene, via proximity effects with topological insulators, could create a novel 2D system that combines nontrivial spin textures with high electron mobility. To engineer practical spintronics applications with such graphene/topological insulator (Gr/TI) heterostructures, an understanding of the hybrid spin-dependent properties is essential. However, to date, despite the large number of experimental studies on Gr/TI heterostructures reporting a great variety of remarkable (spin) transport phenomena, little is known about the true nature of the spin texture of the interface states as well as their role on the measured properties. Here, we use ab initio simulations and tight-binding models to determine the precise spin texture of electronic states in graphene interfaced with a Bi2Se3 topological insulator. Our calculations predict the emergence of a giant spin lifetime anisotropy in the graphene layer, which should be a measurable hallmark of spin transport in Gr/TI heterostructures and suggest novel types of spin devices. ; ICN2 is funded by the CERCA Programme and Generalitat de Catalunya and is supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2013-0295). The authors acknowledge funding from the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (project no. FIS2015-67767-P MINECO/FEDER, FIS2015-64886-C5-3-P), the Secretaria de Universidades e Investigacion del Departamento de Economia y Conocimiento de la Generalidad de Catalunya (grant nos. 2014 SGR 58 and 2014 SGR 301), the European Union Seventh Framework Programme under grant agreement no. 696656 (Graphene Flagship), and the EU H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598). ; Peer reviewed

arXiv:1206.2154 ; We compute the electron transmission through different types of dangling-bond wire on Si(100)–H (2 × 1). Recent progress in the construction of atomic-size interconnects (Weber et al 2012 Science 335 64) shows the possibility to achieve atomic-size circuits via atomic-size wires using silicon surfaces. Hence, electron transport through quasi-1D Si-based structures is a compelling reality. Prior to these achievements, wires formed by controlled desorption of passivating H atoms off the monohydride Si(100) surface have been shown to be subject to 1D correlations and instabilities (Hitosugi et al 1999 Phys. Rev. Lett. 82 4034). The present calculations are based on density functional theory and evaluate the electron transmission though the minimum-energy 1D structures that can be formed when creating dangling-bonds on Si(100)-(2 × 1)-H. The purpose of this study is twofold: (i) to assess the transport properties of these atomic-size wires in the presence of 1D instabilities; (ii) to provide a fingerprint for experimental identification of the instability through the transport characteristics of the wires. To these aims, we evaluate the electron transport through the wires in the absence of instabilities, in the presence of distortions (Jahn–Teller instabilities) and in the presence of magnetic instabilities (ferro- and antiferro-ordering). We find that instabilities substantially reduce the transport capabilities of dangling-bond wires leading to transmissions that vary so differently with electron energy that an unambiguous identification of the wire type should be accessible in transport experiments. ; This work has been supported by the European Union Integrated Project AtMol (http://www.atmol.eu). ; Peer Reviewed

[EN] Magnetic hyperthermia and magnetic resonance imaging (MRI) are two of the most important biomedical applications of magnetic nanoparticles (MNPs). However, the design of MNPs with good heating performance for hyperthermia and dual T1/T2 contrast for MRI remains a considerable challenge. In this work, ultrasmall superparamagnetic iron oxide nanoparticles (USPIONs) are synthesized through a simple one-step methodology. A post-synthetic purification strategy has been implemented in order to separate discrete nanoparticles from aggregates and unstable nanoparticles, leading to USPIONs that preserve chemical and colloidal stability for extended periods of time. The optimized nanoparticles exhibit high saturation magnetization and show good heating efficiency in magnetic hyperthermia experiments. Remarkably, the evaluation of the USPIONs as MRI contrast agents revealed that the nanoparticles are also able to provide significant dual T1/T2 signal enhancement. These promising results demonstrate that USPIONs are excellent candidates for the development of theranostic nanodevices with potential application in both hyperthermia and dual T1/T2 MR imaging. ; We are grateful to the Spanish Government (projects MAT2015-64139-C4-1-R and AGL2015-70235-C2-2-R (MINECO/FEDER)) and the Generalitat Valenciana (Projects PROMETEO/2018/024 and PROMETEOII/2014/047) for financial support. S. S. C. is grateful to the Spanish MEC for his FPU grant. JG acknowledges funding from FCT and the ERDF through NORTE2020 through the project Self-reporting immunestimulating formulation for on-demand cancer therapy with real-time treatment response monitoring (028052). ; Sánchez-Cabezas, S.; Montes-Robles, R.; Gallo, J.; Sancenón Galarza, F.; Martínez-Máñez, R. (2019). Combining magnetic hyperthermia and dual T1/T2 MR imaging using highly versatile iron oxide nanoparticles. Dalton Transactions. 48(12):3883-3892. https://doi.org/10.1039/c8dt04685a ; S ; 3883 ; 3892 ; 48 ; 12 ; Lee, J.-H., Jang, J., Choi, J., Moon, S. H., Noh, S., Kim, J., … Cheon, ...

Heterogeneous atomic magnetic chains are built by atom manipulation on a Cu2N/Cu (100) substrate. Their magnetic properties are studied and rationalized by a combined scanning tunneling microscopy (STM) and density functional theory (DFT) work completed by model Hamiltonian studies. The chains are built using Fe and Mn atoms ontop of the Cu atoms along the N rows of the Cu2N surface. Here, we present results for FeMnx chains (x=1-6) emphasizing the evolution of the geometrical, electronic, and magnetic properties with chain size. By fitting our results to a Heisenberg Hamiltonian we have studied the exchange-coupling matrix elements J for different chains. For the shorter chains, x≤2, we have included spin-orbit effects in the DFT calculations, extracting the magnetic anisotropy energy. Our results are also fitted to a simple anisotropic spin Hamiltonian and we have extracted values for the longitudinal-anisotropy D and transversal-anisotropy E constants. These parameters together with the values for J allow us to compute the magnetic excitation energies of the system and to compare them with the experimental data. ; D.-J.C. acknowledges the European Union for support under the H2020-MSCA-IF-2014 Marie-Curie Individual Fellowship programme Proposal No. 654469 and a previous postdoctoral fellowhship from the Alexander von Humboldt foundation. D.-J.C. and S.L. acknowledge Edgar Weckert and Helmut Dosch (Deutsches Elektronen-Synchrotron, Hamburg, Germany) for providing high-stability laboratory space. N.L. acknowledges financial support from Spanish MINECO (Grant No. MAT2015-66888-C3-2-R). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant No. SEV-2013-0295). ; Peer Reviewed

Monolayers of transition-metal dichalcogenide semiconductors present spin-valley locked electronic bands, a property with applications in valleytronics and spintronics that is usually believed to be absent in their centrosymmetric (as the bilayer or bulk) counterparts. Here we show that bulk 2H-MoS2 hides a spin-polarized nature of states determining its direct band gap, with the spin sequence of valence and conduction bands expected for its single layer. This relevant finding is attained by investigating the behavior of the binding energy of A and B excitons under high pressure, by means of absorption measurements and density-functional-theory calculations. These results raise an unusual situation in which bright and dark exciton degeneracy is naturally broken in a centrosymmetric material. Additionally, the phonon-assisted scattering process of excitons has been studied by analyzing the pressure dependence of the linewidth of discrete excitons observed at the absorption coefficient edge of 2H-MoS2. Also, the pressure dependence of the indirect optical transitions of bulk 2H-MoS2 has been analyzed by absorption measurements and density-functional-theory calculations. These results reflect a progressive closure of the indirect band gap as pressure increases, indicating that metallization of bulk MoS2 may occur at pressures higher than 26 GPa. ; Work inValenciawas supported by the SpanishGovernment (Grants No. TEC2014-53727-C2-1-R and No. MAT2016- 75586-C4-1-P) and the Generalitat Valenciana (Grant No. PROMETEOII/2014/059). Work in Bellaterra was supported by Spanish MINECO (Grants No. FIS2015-64886-C5-3-P and No. FIS2015-64886-C5-4-P), and the Severo Ochoa Centers of Excellence Program (Grants No. SEV-2013-0295 and No. SEV-2015-0496), Generalitat de Catalunya (Grant No. 2017SGR1506 and the CERCA Programme) and by the European Union H2020-EINFRA-5-2015 MaX Center of Excellence (Grant No. 676598). M.B.G. acknowledges Fellowship No.UVINV-PREDOC13-110538 under the program "Atracció de Talent, VLC-CAMPUS" of the University of Valencia. ; Peer reviewed

Spin-orbit coupling (SOC) is generally understood as a highly localized interaction within each atom, whereby core electrons holding large J splittings transfer the SOC to the valence electrons of the same atom, while their direct impact on neighbor valence orbitals is usually small. Seivane and Ferrer [Phys. Rev. Lett. 99, 183401 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.183401] proposed an approach within a tight-binding type ab initio framework assuming that the transfer of SOC from core to valence orbitals only takes place when both are on the same atom, leading to the so-called on-site approximation, which then has been successfully applied to a variety of systems. In this work we thoroughly test its general validity by confronting SOC related properties such as spin splittings, spin textures, or magnetic anisotropies calculated under the on-site approximation versus the more general approach where all the contributions to the SOC, including three-center integrals, are explicitly included. After considering a variety of systems with different dimensionalities, all presenting a strong SOC, we conclude that although the on-site approximation often provides accurate results, it breaks down in some systems where 5d electrons are close to the Fermi level due to their strong SOC and moderately large spatial extension. Furthermore, there are a few examples where subtle inaccuracies lead to qualitatively wrong conclusions, the most clear case being the doping of the topological surface state in Bi2Se3(0001). Finally, magnetic anisotropy energies calculated under this approximation tend to be underestimated. ; This work was financially supported by the Spanish MINECO, MICIU, AEI, and EU FEDER (Grants No. MAT2015-66888-C3-1R, No. RTI2018-097895-B-C41, No. PGC2018-094783, No. PGC2018-096955-C43, and No. PGC2018-096955-C44), Generalitat de Catalunya (Grant No. 2017SGR1506), and the EU MaX Center of Excellence (EU-H2020 Grant No. 824143). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and the CERCA Program of Generalitat de Catalunya. ICMAB is supported by the Spanish MICINN through the Severo Ochoa Centers of Excellence Program (Grant No. CEX2019-000917-S). R.C. acknowledges the funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodoswka-Curie Grant Agreement No. 665919. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Herein, we describe the first on-surface preparation of porphyrin nanotapes (Por NTs) on a gold surface. Structural and electronic characterization reveals that the Por NTs carry one unpaired electron at each end, which leads to magnetic end states. This study provides an alternative and versatile route to the fabrication of Por NTs and a detailed atomic-scale characterization of their structural and electronic properties. ; Porphyrin nanotapes (Por NTs) are promising structures for their use as molecular wires thanks to a high degree of π-conjugation, low HOMO—LUMO gaps, and exceptional conductance. Such structures have been prepared in solution, but their on-surface synthesis remains unreported. Here, meso–meso triply fused Por NTs have been prepared through a two-step synthesis on Au(111). The diradical character of the on-surface formed building block PorA2, a phenalenyl π-extended ZnIIPor, facilitates intermolecular homocoupling and allows for the formation of laterally π-extended tapes. The structural and electronic properties of individual Por NTs are addressed, both on Au(111) and on a thin insulating NaCl layer, by high-resolution scanning probe microscopy/spectroscopy complemented by DFT calculations. These Por NTs carry one unpaired electron at each end, which leads to magnetic end states. Our study provides a versatile route towards Por NTs and the atomic-scale characterization of such tapes. ; This work was supported by the Swiss National Science Foundation under Grant No. 200020_182015, the European Union's Horizon 2020 research and innovation programme under grant agreement number 785219 (Graphene Flagship Core 2), the Office of Naval Research (N00014-18-1-2708), MINECO, CTQ2017-85393-P (Phthalophoto, T.T.), and PID2020-116490GB-I00 (Porphyrinoids, T.T., G.B.). IMDEA Nanociencia also acknowledges support from the "Severo Ochoa" Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). R.R. and N.L. are grateful for funding from the EU-FET Open H2020 Mechanics with Molecules project (grant 766864). ; Peer reviewed

On-surface synthesis is becoming an increasingly popular approach to obtain new organic materials. In this context, metallic surfaces are the most commonly used substrates. However, their hybridization with the adsorbates often hinder a proper characterization of the molecule's intrinsic electronic and magnetic properties. Here we report a route to electronically decouple molecules from their supporting substrates. In particular, we have used a Ag(001) substrate and hydrogenated heptacene molecules, in which the longest conjugated segment determining its frontier molecular orbitals amounts to five consecutive rings. The non-planarity that sp3 atoms impose on the carbon backbone results in electronically decoupled molecules, as demonstrated by scanning tunneling spectroscopy measurements. The charging resonances of the latter imply the presence of double tunneling barriers. We further explain the existing relation between the charging resonance energy and their contrast, as well as with the presence or absence of additional Kondo resonances. ; This project has received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement Nos. 635919 (ERC-StG), 837225 (ERC-PoC), and 766864 (FET-Open), from the Spanish Agencia Estatal de Investigación (Grant Nos. MAT2016-78293-C6, PID2019-104815GB-I00 and PID2019-107338RB-C63), from AGAUR (2017 SGR 1257), and from the CERCA,Program/Generalitat de Catalunya. ; Peer reviewed

The interaction among magnetic moments screened by conduction electrons drives quantum phase transitions between magnetically ordered and heavy-fermion ground states. Here, starting from isolated magnetic impurities in the Kondo regime, we investigate the formation of the finite size analogue of a heavy Fermi liquid. We build regularly-spaced chains of Co adatoms on a metallic surface by atomic manipulation. Scanning tunneling spectroscopy is used to obtain maps of the Kondo resonance intensity with sub-atomic resolution. For sufficiently small interatomic separation, the spatial distribution of Kondo screening does not coincide with the position of the adatoms. It also develops enhancements at both edges of the chains. Since we can rule out any other interaction between Kondo impurities, this is explained in terms of the indirect hybridization of the Kondo orbitals mediated by a coherent electron gas, the mechanism that causes the emergence of heavy quasiparticles in the thermodynamic limit. ; Financial support was provided by the Spanish Plan Nacional de I+D+i (grants MAT 2013-46593-C6-3-P, MAT2016-78293-C6-6-R, MAT2015-66888-C3-2-R, and FIS2015-64886-C5-3-P), Charles University (programme PRIMUS/Sci/09) and the European Union through programmes Interreg-POCTEFA (grant TNSI/EFA194/16) and H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598). M.M.-L., M.P., and D.S. acknowledge the use of SAI at Universidad de Zaragoza. R.R. acknowledges The Severo Ochoa Centers of Excellence Program (grant no. SEV-2017-0706) and Generalitat de Catalunya (grant no. 2017SGR1506 and the CERCA Programme). ; Peer reviewed

Development of novel 2D materials with singular and thrilling properties has aroused large interest due to the novel unexpected applications that can be derived from there. In this sense, coordination polymers (CPs) have appeared as matching candidates thanks to their rational chemical design and the added-value properties given by the presence of metal ions. This is the case of switchable spin-crossover systems that have been proposed as excellent candidates for data storage or sensing, among others. Here we report the delamination of crystals of the 2D spin-crossover (SCO) {[Fe(L1)2](ClO4)2}∝ (1) CP by liquid-phase exfoliation (LPE) in water. The application of this top-down technique results in the formation of flakes with controlled thicknesses, down to 1–2 nm thick (mostly mono- and bilayer), that retain the chemical composition and SCO interconversion of the bulk material. Moreover, these flakes can be handled as stable colloidal dispersions for many days. This allows for a controlled transfer to solid substrates and the formation of thermochromic polymeric films as a proof-of-concept of device. These first results will definitely open new venues and opportunities for the investigation and future integration of these original switchable 2D materials in devices. ; This work was supported by projects MAT2015-70615-R, CTQ2015-65439-R, and FIS2015-64886-C5-3-P from the Spanish Government funds and by European Regional Development Fund (ERDF). Funded by the CERCA Program/Generalitat de Catalunya. ICN2 is supported by the Severo Ochoa program from Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant SEV-2013-0295). Funded by the project 2014-SGR-301 (Generalitat de Catalunya). This work was supported by the Fonds National de la Recherche Scientifique-FNRS (PDR T.0102.15) and COST actions CM1305 and CA15128. M. M. D is a chargé de recherches from the F.R.S.-FNRS. S.S.-G. acknowledges the support from MINECO BES-2015-071492 grant. R.R. and P.O. acknowledge support from EU H2020-EINFRA-5-2015 MaX Center of Excellence (Grant 676598). ; Peer reviewed